diff --git a/example/src/tests.ts b/example/src/tests.ts
index 814a091b3..1dff64244 100644
--- a/example/src/tests.ts
+++ b/example/src/tests.ts
@@ -869,3 +869,59 @@ test('returns keyMaterial for conversations', async () => {
 
   return true
 })
+
+test('correctly handles lowercase addresses', async () => {
+  const bob = await Client.createRandom({ env: 'local' })
+  await delayToPropogate()
+  const alice = await Client.createRandom({ env: 'local' })
+  await delayToPropogate()
+  if (bob.address === alice.address) {
+    throw new Error('bob and alice should be different')
+  }
+
+  const bobConversation = await bob.conversations.newConversation(
+    alice.address.toLocaleLowerCase()
+  )
+  await delayToPropogate()
+  if (!bobConversation) {
+    throw new Error('bobConversation should exist')
+  }
+  const aliceConversation = (await alice.conversations.list())[0]
+  if (!aliceConversation) {
+    throw new Error('aliceConversation should exist')
+  }
+
+  await bob.contacts.deny([aliceConversation.peerAddress.toLocaleLowerCase()])
+  await delayToPropogate()
+  const deniedState = await bob.contacts.isDenied(aliceConversation.peerAddress)
+  const allowedState = await bob.contacts.isAllowed(
+    aliceConversation.peerAddress
+  )
+  if (!deniedState) {
+    throw new Error(`contacts denied by bo should be denied not ${deniedState}`)
+  }
+
+  if (allowedState) {
+    throw new Error(
+      `contacts denied by bo should be denied not ${allowedState}`
+    )
+  }
+  const deniedLowercaseState = await bob.contacts.isDenied(
+    aliceConversation.peerAddress.toLocaleLowerCase()
+  )
+  const allowedLowercaseState = await bob.contacts.isAllowed(
+    aliceConversation.peerAddress.toLocaleLowerCase()
+  )
+  if (!deniedLowercaseState) {
+    throw new Error(
+      `contacts denied by bo should be denied not ${deniedLowercaseState}`
+    )
+  }
+
+  if (allowedLowercaseState) {
+    throw new Error(
+      `contacts denied by bo should be denied not ${allowedLowercaseState}`
+    )
+  }
+  return true
+})
diff --git a/package.json b/package.json
index c21ef743b..24ebc7f2b 100644
--- a/package.json
+++ b/package.json
@@ -46,8 +46,10 @@
   "dependencies": {
     "@ethersproject/bytes": "^5.7.0",
     "@msgpack/msgpack": "^3.0.0-beta2",
+    "@noble/hashes": "^1.3.3",
     "@xmtp/proto": "^3.25.0",
-    "buffer": "^6.0.3"
+    "buffer": "^6.0.3",
+    "text-encoding": "^0.7.0"
   },
   "devDependencies": {
     "@babel/plugin-proposal-export-namespace-from": "^7.18.9",
diff --git a/src/index.ts b/src/index.ts
index b2039c9ef..7d0e2854f 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -14,6 +14,7 @@ import {
 import { Conversation } from './lib/Conversation'
 import { DecodedMessage } from './lib/DecodedMessage'
 import type { Query } from './lib/Query'
+import { getAddress } from './utils/address'
 
 export { ReactionCodec } from './lib/NativeCodecs/ReactionCodec'
 export { ReplyCodec } from './lib/NativeCodecs/ReplyCodec'
@@ -105,7 +106,7 @@ export async function canMessage(
   clientAddress: string,
   peerAddress: string
 ): Promise<boolean> {
-  return await XMTPModule.canMessage(clientAddress, peerAddress)
+  return await XMTPModule.canMessage(clientAddress, getAddress(peerAddress))
 }
 
 export async function staticCanMessage(
@@ -113,7 +114,11 @@ export async function staticCanMessage(
   environment: 'local' | 'dev' | 'production',
   appVersion?: string | undefined
 ): Promise<boolean> {
-  return await XMTPModule.staticCanMessage(peerAddress, environment, appVersion)
+  return await XMTPModule.staticCanMessage(
+    getAddress(peerAddress),
+    environment,
+    appVersion
+  )
 }
 
 export async function encryptAttachment(
@@ -212,7 +217,7 @@ export async function createConversation<ContentTypes>(
     JSON.parse(
       await XMTPModule.createConversation(
         client.address,
-        peerAddress,
+        getAddress(peerAddress),
         JSON.stringify(context || {})
       )
     )
diff --git a/src/lib/Contacts.ts b/src/lib/Contacts.ts
index 3ea970f9f..9488fa115 100644
--- a/src/lib/Contacts.ts
+++ b/src/lib/Contacts.ts
@@ -1,6 +1,7 @@
 import { Client } from './Client'
 import { ConsentListEntry } from './ConsentListEntry'
 import * as XMTPModule from '../index'
+import { getAddress } from '../utils/address'
 
 export default class Contacts {
   client: Client<any>
@@ -10,19 +11,27 @@ export default class Contacts {
   }
 
   async isAllowed(address: string): Promise<boolean> {
-    return await XMTPModule.isAllowed(this.client.address, address)
+    return await XMTPModule.isAllowed(this.client.address, getAddress(address))
   }
 
   async isDenied(address: string): Promise<boolean> {
-    return await XMTPModule.isDenied(this.client.address, address)
+    return await XMTPModule.isDenied(this.client.address, getAddress(address))
   }
 
   async deny(addresses: string[]): Promise<void> {
-    return await XMTPModule.denyContacts(this.client.address, addresses)
+    const checkSummedAddresses = addresses.map((address) => getAddress(address))
+    return await XMTPModule.denyContacts(
+      this.client.address,
+      checkSummedAddresses
+    )
   }
 
   async allow(addresses: string[]): Promise<void> {
-    return await XMTPModule.allowContacts(this.client.address, addresses)
+    const checkSummedAddresses = addresses.map((address) => getAddress(address))
+    return await XMTPModule.allowContacts(
+      this.client.address,
+      checkSummedAddresses
+    )
   }
 
   async refreshConsentList(): Promise<ConsentListEntry[]> {
diff --git a/src/lib/Conversations.ts b/src/lib/Conversations.ts
index 4b13f7352..9363071b5 100644
--- a/src/lib/Conversations.ts
+++ b/src/lib/Conversations.ts
@@ -3,6 +3,7 @@ import { Conversation } from './Conversation'
 import { DecodedMessage } from './DecodedMessage'
 import { ConversationContext } from '../XMTP.types'
 import * as XMTPModule from '../index'
+import { getAddress } from '../utils/address'
 
 export default class Conversations<ContentTypes> {
   client: Client<ContentTypes>
@@ -50,9 +51,10 @@ export default class Conversations<ContentTypes> {
     peerAddress: string,
     context?: ConversationContext
   ): Promise<Conversation<ContentTypes>> {
+    const checksumAddress = getAddress(peerAddress)
     return await XMTPModule.createConversation(
       this.client,
-      peerAddress,
+      checksumAddress,
       context
     )
   }
diff --git a/src/utils/address.ts b/src/utils/address.ts
new file mode 100644
index 000000000..cbca82c70
--- /dev/null
+++ b/src/utils/address.ts
@@ -0,0 +1,50 @@
+import { keccak_256 } from '@noble/hashes/sha3'
+import { TextEncoder } from 'text-encoding'
+
+const addressRegex = /^0x[a-fA-F0-9]{40}$/
+const encoder = new TextEncoder()
+
+export function stringToBytes(value: string): Uint8Array {
+  const bytes = encoder.encode(value)
+  return bytes
+}
+
+export function keccak256(value: Uint8Array): Uint8Array {
+  const bytes = keccak_256(value)
+  return bytes
+}
+
+export function isAddress(address: string): boolean {
+  return addressRegex.test(address)
+}
+
+export function checksumAddress(address_: string, chainId?: number): string {
+  const hexAddress = chainId
+    ? `${chainId}${address_.toLowerCase()}`
+    : address_.substring(2).toLowerCase()
+  const hash = keccak256(stringToBytes(hexAddress))
+
+  const address = (
+    chainId ? hexAddress.substring(`${chainId}0x`.length) : hexAddress
+  ).split('')
+  for (let i = 0; i < 40; i += 2) {
+    if (hash[i >> 1] >> 4 >= 8 && address[i]) {
+      address[i] = address[i].toUpperCase()
+    }
+    if ((hash[i >> 1] & 0x0f) >= 8 && address[i + 1]) {
+      address[i + 1] = address[i + 1].toUpperCase()
+    }
+  }
+
+  return `0x${address.join('')}`
+}
+
+const addressCache = new Map<string, string>()
+
+export function getAddress(address: string, chainId?: number): string {
+  if (addressCache.has(address)) return addressCache.get(address) as string
+  if (!isAddress(address)) throw new Error('Invalid address' + address)
+  const checksumedAddress = checksumAddress(address, chainId)
+  addressCache.set(address, checksumedAddress)
+  return checksumedAddress
+}
diff --git a/yarn.lock b/yarn.lock
index e7dff4aa2..672097565 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1536,7 +1536,7 @@
   resolved "https://registry.yarnpkg.com/@noble/hashes/-/hashes-1.3.2.tgz#6f26dbc8fbc7205873ce3cee2f690eba0d421b39"
   integrity sha512-MVC8EAQp7MvEcm30KWENFjgR+Mkmf+D189XJTkFIlwohU5hcBbn1ZkKq7KVTi2Hme3PMGF390DaL52beVrIihQ==
 
-"@noble/hashes@~1.3.0", "@noble/hashes@~1.3.2":
+"@noble/hashes@^1.3.3", "@noble/hashes@~1.3.0", "@noble/hashes@~1.3.2":
   version "1.3.3"
   resolved "https://registry.yarnpkg.com/@noble/hashes/-/hashes-1.3.3.tgz#39908da56a4adc270147bb07968bf3b16cfe1699"
   integrity sha512-V7/fPHgl+jsVPXqqeOzT8egNj2iBIVt+ECeMMG8TdcnTikP3oaBtUVqpT/gYCR68aEBJSF+XbYUxStjbFMqIIA==
@@ -7958,6 +7958,11 @@ test-exclude@^6.0.0:
     glob "^7.1.4"
     minimatch "^3.0.4"
 
+text-encoding@^0.7.0:
+  version "0.7.0"
+  resolved "https://registry.yarnpkg.com/text-encoding/-/text-encoding-0.7.0.tgz#f895e836e45990624086601798ea98e8f36ee643"
+  integrity sha512-oJQ3f1hrOnbRLOcwKz0Liq2IcrvDeZRHXhd9RgLrsT+DjWY/nty1Hi7v3dtkaEYbPYe0mUoOfzRrMwfXXwgPUA==
+
 text-extensions@^2.0.0:
   version "2.4.0"
   resolved "https://registry.yarnpkg.com/text-extensions/-/text-extensions-2.4.0.tgz#a1cfcc50cf34da41bfd047cc744f804d1680ea34"