diff --git a/changelog.d/20231213_145052_bjorn.wilhelm.kihlberg_PLT_7701.md b/changelog.d/20231213_145052_bjorn.wilhelm.kihlberg_PLT_7701.md
new file mode 100644
index 00000000..9f08c0c4
--- /dev/null
+++ b/changelog.d/20231213_145052_bjorn.wilhelm.kihlberg_PLT_7701.md
@@ -0,0 +1,6 @@
+### @marlowe.io/runtime-rest-client
+
+- PLT-7701: Extend the rest client with procedure `getContractSourceById`. (Implemented in [PR-128](https://github.com/input-output-hk/marlowe-ts-sdk/pull/128))
+- PLT-7702: Extend the rest client with procedure `getContractSourceAdjacency`. (Implemented in [PR-128](https://github.com/input-output-hk/marlowe-ts-sdk/pull/128))
+- PLT-7703: Extend the rest client with procedure `getContractSourceClosure`. (Implemented in [PR-128](https://github.com/input-output-hk/marlowe-ts-sdk/pull/128))
+- PLT-8427: Extend the rest client with procedure `getNextStepsForContract`. (Implemented in [PR-128](https://github.com/input-output-hk/marlowe-ts-sdk/pull/128))
diff --git a/examples/js/poc-helpers.js b/examples/js/poc-helpers.js
index 6c879970..19c28a30 100644
--- a/examples/js/poc-helpers.js
+++ b/examples/js/poc-helpers.js
@@ -39,7 +39,7 @@ export function logJSON(message, json) {
 export function getRuntimeUrl() {
   const runtimeUrlInput = document.getElementById("runtimeUrl");
   return (
-    runtimeUrlInput.value ||
+    (runtimeUrlInput && runtimeUrlInput.value) ||
     "https://marlowe-runtime-preprod-web.demo.scdev.aws.iohkdev.io/"
   );
 }
diff --git a/examples/rest-client-flow/index.html b/examples/rest-client-flow/index.html
index 0ee0f410..c15c20a5 100644
--- a/examples/rest-client-flow/index.html
+++ b/examples/rest-client-flow/index.html
@@ -135,6 +135,43 @@ <h2>Request</h2>
         >/contracts/:contractId/transactions/:transactionId</a
       >
       <br />
+      <input
+        id="getContractSourceById"
+        type="button"
+        value="Get contract source by contract Source id"
+        class="endpoint"
+      />
+      GETs contract source by contract Source ID
+      <a
+        href="https://input-output-hk.github.io/marlowe-ts-sdk/interfaces/_marlowe_io_runtime_rest_client.index.RestClient.html#getContractSourceById"
+        >/contracts/sources/:contractSourceId</a
+      >
+      <br />
+      <input
+        id="getContractSourceAdjacency"
+        type="button"
+        value="Get adjacent contract Source IDs"
+        class="endpoint"
+      />
+      GETs the contract Source IDs which are adjacent to a contract
+      <a
+        href="https://input-output-hk.github.io/marlowe-ts-sdk/interfaces/_marlowe_io_runtime_rest_client.index.RestClient.html#getContractSourceAdjacency"
+        >/contracts/sources/:contractSourceId/adjacency</a
+      >
+      <br />
+      <input
+        id="getContractSourceClosure"
+        type="button"
+        value="Get contract Source IDs in contract"
+        class="endpoint"
+      />
+      GETs the contract Source IDs which appear in the full hierarchy of a
+      contract source
+      <a
+        href="https://input-output-hk.github.io/marlowe-ts-sdk/interfaces/_marlowe_io_runtime_rest_client.index.RestClient.html#getContractSourceClosure"
+        >/contracts/sources/:contractSourceId/closure</a
+      >
+      <br />
     </div>
 
     <h2>Console</h2>
diff --git a/packages/marlowe-object/src/index.ts b/packages/marlowe-object/src/index.ts
index 30045999..a2cc29f8 100644
--- a/packages/marlowe-object/src/index.ts
+++ b/packages/marlowe-object/src/index.ts
@@ -1,6 +1,11 @@
 export { Action, Deposit, Notify, Choice } from "./actions.js";
 export { ChoiceName, ChoiceId, Bound, ChosenNum } from "./choices.js";
-export { Reference, Label } from "./reference.js";
+export {
+  Reference,
+  Label,
+  ContractSourceId,
+  ContractSourceIdGuard,
+} from "./reference.js";
 export { Address, Role, Party } from "./participants.js";
 export { Payee, PayeeAccount, PayeeParty, AccountId } from "./payee.js";
 
diff --git a/packages/marlowe-object/src/reference.ts b/packages/marlowe-object/src/reference.ts
index 67204e52..ae9e7606 100644
--- a/packages/marlowe-object/src/reference.ts
+++ b/packages/marlowe-object/src/reference.ts
@@ -8,6 +8,14 @@ export type Label = string;
 
 export const LabelGuard: t.Type<Label> = t.string;
 
+/**
+ * A label for one of the {@link ObjectType}
+ * @category Object
+ */
+export type ContractSourceId = string;
+
+export const ContractSourceIdGuard: t.Type<ContractSourceId> = t.string;
+
 /**
  * A reference to an {@link ObjectType}.
  * @category Object
@@ -20,4 +28,6 @@ export interface Reference {
  * {@link !io-ts-usage | Dynamic type guard} for the {@link Reference | reference type}.
  * @category Object
  */
-export const ReferenceGuard: t.Type<Reference> = t.type({ ref: t.string });
+export const ReferenceGuard: t.Type<Reference> = t.type({
+  ref: ContractSourceIdGuard,
+});
diff --git a/packages/runtime/client/rest/src/contract/endpoints/sources.ts b/packages/runtime/client/rest/src/contract/endpoints/sources.ts
index e8b098c6..a4bb3721 100644
--- a/packages/runtime/client/rest/src/contract/endpoints/sources.ts
+++ b/packages/runtime/client/rest/src/contract/endpoints/sources.ts
@@ -4,21 +4,26 @@ import * as E from "fp-ts/lib/Either.js";
 import { pipe } from "fp-ts/lib/function.js";
 import { formatValidationErrors } from "jsonbigint-io-ts-reporters";
 
-import { BuiltinByteString } from "@marlowe.io/language-core-v1";
-import { Bundle, Label } from "@marlowe.io/marlowe-object";
+import { Contract } from "@marlowe.io/language-core-v1";
+import {
+  Bundle,
+  Label,
+  ContractSourceId,
+  ContractSourceIdGuard,
+} from "@marlowe.io/marlowe-object";
 import { AxiosInstance } from "axios";
 
 export interface CreateContractSourcesResponse {
-  contractSourceId: BuiltinByteString;
+  contractSourceId: ContractSourceId;
   intermediateIds: {
-    [key: Label]: BuiltinByteString;
+    [key: Label]: ContractSourceId;
   };
 }
 
 const CreateContractSourcesResponseGuard: t.Type<CreateContractSourcesResponse> =
   t.type({
-    contractSourceId: G.BuiltinByteString,
-    intermediateIds: t.record(t.string, G.BuiltinByteString),
+    contractSourceId: ContractSourceIdGuard,
+    intermediateIds: t.record(t.string, ContractSourceIdGuard),
   });
 
 export const createContractSources = (axiosInstance: AxiosInstance) => {
@@ -40,3 +45,94 @@ export const createContractSources = (axiosInstance: AxiosInstance) => {
     );
   };
 };
+
+export interface GetContractBySourceIdRequest {
+  contractSourceId: ContractSourceId;
+  expand?: boolean;
+}
+
+export type GetContractBySourceIdResponse = Contract;
+
+const GetContractBySourceIdResponseGuard: t.Type<GetContractBySourceIdResponse> =
+  G.Contract;
+
+export const getContractSourceById =
+  (axiosInstance: AxiosInstance) =>
+  async ({
+    contractSourceId,
+    expand,
+  }: GetContractBySourceIdRequest): Promise<GetContractBySourceIdResponse> => {
+    const response = await axiosInstance.get(
+      `/contracts/sources/${encodeURIComponent(contractSourceId)}`,
+      { params: { expand } }
+    );
+    return pipe(
+      GetContractBySourceIdResponseGuard.decode(response.data),
+      E.match(
+        (e) => {
+          throw formatValidationErrors(e);
+        },
+        (e) => e
+      )
+    );
+  };
+
+export interface GetContractSourceAdjacencyRequest {
+  contractSourceId: ContractSourceId;
+}
+
+export interface GetContractSourceAdjacencyResponse {
+  results: ContractSourceId[];
+}
+
+const GetContractSourceAdjacencyResponseGuard: t.Type<GetContractSourceAdjacencyResponse> =
+  t.type({ results: t.array(ContractSourceIdGuard) });
+
+export const getContractSourceAdjacency =
+  (axiosInstance: AxiosInstance) =>
+  async ({
+    contractSourceId,
+  }: GetContractSourceAdjacencyRequest): Promise<GetContractSourceAdjacencyResponse> => {
+    const response = await axiosInstance.get(
+      `/contracts/sources/${encodeURIComponent(contractSourceId)}/adjacency`
+    );
+    return pipe(
+      GetContractSourceAdjacencyResponseGuard.decode(response.data),
+      E.match(
+        (e) => {
+          throw formatValidationErrors(e);
+        },
+        (e) => e
+      )
+    );
+  };
+
+export interface GetContractSourceClosureRequest {
+  contractSourceId: ContractSourceId;
+}
+
+export interface GetContractSourceClosureResponse {
+  results: ContractSourceId[];
+}
+
+const GetContractSourceClosureResponseGuard: t.Type<GetContractSourceClosureResponse> =
+  t.type({ results: t.array(ContractSourceIdGuard) });
+
+export const getContractSourceClosure =
+  (axiosInstance: AxiosInstance) =>
+  async ({
+    contractSourceId,
+  }: GetContractSourceClosureRequest): Promise<GetContractSourceClosureResponse> => {
+    const response = await axiosInstance.get(
+      `/contracts/sources/${encodeURIComponent(contractSourceId)}/closure`
+    );
+    return pipe(
+      GetContractSourceClosureResponseGuard.decode(response.data),
+      E.match(
+        (e) => {
+          throw formatValidationErrors(e);
+        },
+        (e) => e
+      )
+    );
+  };
diff --git a/packages/runtime/client/rest/src/contract/next/endpoint.ts b/packages/runtime/client/rest/src/contract/next/endpoint.ts
index da479456..62bdaec7 100644
--- a/packages/runtime/client/rest/src/contract/next/endpoint.ts
+++ b/packages/runtime/client/rest/src/contract/next/endpoint.ts
@@ -40,3 +40,48 @@ export const getViaAxios: (axiosInstance: AxiosInstance) => GET =
 
 const contractNextEndpoint = (contractId: ContractId): string =>
   `/contracts/${encodeURIComponent(unContractId(contractId))}/next`;
+
+export interface GetNextStepsForContractRequest {
+  contractId: ContractId;
+  validityStart: bigint;
+  validityEnd: bigint;
+  parties?: Party[];
+}
+
+export type GetNextStepsForContractResponse = Next;
+
+const GetNextStepsForContractResponseGuard = Next;
+
+export const getNextStepsForContract =
+  (axiosInstance: AxiosInstance) =>
+  async ({
+    contractId,
+    validityStart,
+    validityEnd,
+    parties,
+  }: GetNextStepsForContractRequest): Promise<GetNextStepsForContractResponse> => {
+    const response = await axiosInstance.get(
+      `/contracts/${encodeURIComponent(
+        unContractId(contractId)
+      )}/next?${stringify({
+        validityStart: posixTimeToIso8601(validityStart),
+        validityEnd: posixTimeToIso8601(validityEnd),
+        party: parties,
+      })}`,
+      {
+        headers: {
+          Accept: "application/json",
+          "Content-Type": "application/json",
+        },
+      }
+    );
+    return pipe(
+      GetNextStepsForContractResponseGuard.decode(response.data),
+      E.match(
+        (e) => {
+          throw formatValidationErrors(e);
+        },
+        (e) => e
+      )
+    );
+  };
diff --git a/packages/runtime/client/rest/src/index.ts b/packages/runtime/client/rest/src/index.ts
index 35a2d11e..9d378452 100644
--- a/packages/runtime/client/rest/src/index.ts
+++ b/packages/runtime/client/rest/src/index.ts
@@ -27,8 +27,8 @@ import * as Contracts from "./contract/endpoints/collection.js";
 import * as Transaction from "./contract/transaction/endpoints/singleton.js";
 import * as Transactions from "./contract/transaction/endpoints/collection.js";
 import * as Sources from "./contract/endpoints/sources.js";
+import * as Next from "./contract/next/endpoint.js";
 import { TransactionsRange } from "./contract/transaction/endpoints/collection.js";
-import * as ContractNext from "./contract/next/endpoint.js";
 import { unsafeTaskEither } from "@marlowe.io/adapter/fp-ts";
 import {
   ContractId,
@@ -40,8 +40,6 @@ import {
 import { submitContractViaAxios } from "./contract/endpoints/singleton.js";
 import { ContractDetails } from "./contract/details.js";
 import { TransactionDetails } from "./contract/transaction/details.js";
-import { CreateContractSourcesResponse } from "./contract/endpoints/sources.js";
-import { BuildCreateContractTxRequestWithContract } from "./contract/index.js";
 // import curlirize from 'axios-curlirize';
 
 /**
@@ -89,7 +87,44 @@ export interface RestClient {
   createContractSources(
     mainId: Label,
     bundle: Bundle
-  ): Promise<CreateContractSourcesResponse>;
+  ): Promise<Sources.CreateContractSourcesResponse>;
+
+  /**
+   * Gets the contract associated with given source id
+   * @throws DecodingError - If the response from the server can't be decoded
+   * @see {@link https://docs.marlowe.iohk.io/api/get-contract-source-by-id | The backend documentation}
+   */
+  getContractSourceById(
+    request: Sources.GetContractBySourceIdRequest
+  ): Promise<Sources.GetContractBySourceIdResponse>;
+
+  /**
+   * Get the contract source IDs which are adjacent to a contract source (they appear directly in the contract source).
+   * @throws DecodingError - If the response from the server can't be decoded
+   * @see {@link https://docs.marlowe.iohk.io/api/get-adjacent-contract-source-i-ds-by-id | The backend documentation}
+   */
+  getContractSourceAdjacency(
+    request: Sources.GetContractSourceAdjacencyRequest
+  ): Promise<Sources.GetContractSourceAdjacencyResponse>;
+
+  /**
+   * Get the contract source IDs which appear in the full hierarchy of a contract source (including the ID of the contract source itself).
+   * @throws DecodingError - If the response from the server can't be decoded
+   * @see {@link https://docs.marlowe.iohk.io/api/get-contract-source-closure-by-id | The backend documentation}
+   */
+  getContractSourceClosure(
+    request: Sources.GetContractSourceClosureRequest
+  ): Promise<Sources.GetContractSourceClosureResponse>;
+
+  /**
+   * Get inputs which could be performed on a contract within a time range by the requested parties.
+   * @throws DecodingError - If the response from the server can't be decoded
+   * @see {@link https://docs.marlowe.iohk.io/api/get-next-contract-steps | The backend documentation}
+   */
+  getNextStepsForContract(
+    request: Next.GetNextStepsForContractRequest
+  ): Promise<Next.GetNextStepsForContractResponse>;
+
   /**
    * Gets a single contract by id
    * @param contractId The id of the contract to get
@@ -97,6 +132,7 @@ export interface RestClient {
    * @see {@link https://docs.marlowe.iohk.io/api/get-contract-by-id | The backend documentation}
    */
   getContractById(contractId: ContractId): Promise<ContractDetails>;
+
   /**
    * Submits a signed contract creation transaction
    * @see {@link https://docs.marlowe.iohk.io/api/submit-contract-to-chain | The backend documentation}
@@ -105,6 +141,7 @@ export interface RestClient {
     contractId: ContractId,
     txEnvelope: TextEnvelope
   ): Promise<void>;
+
   /**
    * Gets a paginated list of  {@link contract.TxHeader } for a given contract.
    * @see {@link https://docs.marlowe.iohk.io/api/get-transactions-for-contract | The backend documentation }
@@ -116,6 +153,7 @@ export interface RestClient {
     contractId: ContractId,
     range?: TransactionsRange
   ): Promise<Transactions.GetTransactionsForContractResponse>;
+
   /**
    * Create an unsigned transaction which applies inputs to a contract.
    * @see {@link https://docs.marlowe.iohk.io/api/apply-inputs-to-contract | The backend documentation}
@@ -126,6 +164,7 @@ export interface RestClient {
   applyInputsToContract(
     request: Transactions.ApplyInputsToContractRequest
   ): Promise<Transactions.TransactionTextEnvelope>;
+
   //   getTransactionById: Transaction.GET; // - https://docs.marlowe.iohk.io/api/get-transaction-by-id
   /**
    * Submit a signed transaction (generated with {@link @marlowe.io/runtime-rest-client!index.RestClient#applyInputsToContract} and signed with the {@link @marlowe.io/wallet!api.WalletAPI#signTx} procedure) that applies inputs to a contract.
@@ -195,13 +234,6 @@ export interface RestClient {
    */
   healthcheck(): Promise<Boolean>;
 
-  //   getNextStepsForContract: Next.GET; // - Jamie, is it this one? https://docs.marlowe.iohk.io/api/get-transaction-output-by-id? if so lets unify
-
-  //   postContractSource: ContractSources.POST; // - Jamie, is it this one? https://docs.marlowe.iohk.io/api/access-contract-import if so lets unify
-  //   getContractSource: ContractSource.GET; // - Jamie, is it this one? https://docs.marlowe.iohk.io/api/get-contract-import-by-id
-  //   getContractAdjacency: ContractSource.GET_ADJACENCY;  // - Jamie, is it this one? https://docs.marlowe.iohk.io/api/get-adjacency-by-id if so lets unify
-  //   getContractClosure: ContractSource.GET_CLOSURE; // Jamie is it this one? - https://docs.marlowe.iohk.io/api/get-closure-by-id
-
   /**
    * Get payouts to parties from role-based contracts.
    * @see {@link https://docs.marlowe.iohk.io/api/get-role-payouts | The backend documentation}
@@ -280,6 +312,18 @@ export function mkRestClient(baseURL: string): RestClient {
     createContractSources(mainId, bundle) {
       return Sources.createContractSources(axiosInstance)(mainId, bundle);
     },
+    getContractSourceById(request) {
+      return Sources.getContractSourceById(axiosInstance)(request);
+    },
+    getContractSourceAdjacency(request) {
+      return Sources.getContractSourceAdjacency(axiosInstance)(request);
+    },
+    getContractSourceClosure(request) {
+      return Sources.getContractSourceClosure(axiosInstance)(request);
+    },
+    getNextStepsForContract(request) {
+      return Next.getNextStepsForContract(axiosInstance)(request);
+    },
     submitContract(contractId, txEnvelope) {
       return submitContractViaAxios(axiosInstance)(contractId, txEnvelope);
     },
@@ -470,7 +514,7 @@ export interface ContractsAPI {
     /**
      * @see {@link }
      */
-    next: ContractNext.GET;
+    next: Next.GET;
     transactions: {
       /**
        * @see {@link }
@@ -550,7 +594,7 @@ export function mkFPTSRestClient(baseURL: string): FPTSRestAPI {
       contract: {
         get: Contract.getViaAxios(axiosInstance),
         put: Contract.putViaAxios(axiosInstance),
-        next: ContractNext.getViaAxios(axiosInstance),
+        next: Next.getViaAxios(axiosInstance),
         transactions: {
           getHeadersByRange:
             Transactions.getHeadersByRangeViaAxios(axiosInstance),