diff --git a/examples/rag/main.go b/examples/rag/simple/main.go
similarity index 100%
rename from examples/rag/main.go
rename to examples/rag/simple/main.go
diff --git a/examples/rag/subdocument/main.go b/examples/rag/subdocument/main.go
new file mode 100644
index 00000000..ad41628f
--- /dev/null
+++ b/examples/rag/subdocument/main.go
@@ -0,0 +1,54 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/henomis/lingoose/assistant"
+	openaiembedder "github.com/henomis/lingoose/embedder/openai"
+	"github.com/henomis/lingoose/index"
+	"github.com/henomis/lingoose/index/vectordb/jsondb"
+	"github.com/henomis/lingoose/llm/openai"
+	"github.com/henomis/lingoose/rag"
+	"github.com/henomis/lingoose/thread"
+)
+
+// download https://raw.githubusercontent.com/hwchase17/chat-your-data/master/state_of_the_union.txt
+
+func main() {
+	r := rag.NewSubDocumentRAG(
+		index.New(
+			jsondb.New().WithPersist("db.json"),
+			openaiembedder.New(openaiembedder.AdaEmbeddingV2),
+		),
+		openai.New(),
+	).WithTopK(3)
+
+	_, err := os.Stat("db.json")
+	if os.IsNotExist(err) {
+		err = r.AddSources(context.Background(), "state_of_the_union.txt")
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	a := assistant.New(
+		openai.New().WithTemperature(0),
+	).WithRAG(r).WithThread(
+		thread.New().AddMessages(
+			thread.NewUserMessage().AddContent(
+				thread.NewTextContent("what is the purpose of NATO?"),
+			),
+		),
+	)
+
+	err = a.Run(context.Background())
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Println("----")
+	fmt.Println(a.Thread())
+	fmt.Println("----")
+}
diff --git a/rag/rag.go b/rag/rag.go
index c8f3d529..a4dd8eda 100644
--- a/rag/rag.go
+++ b/rag/rag.go
@@ -35,11 +35,6 @@ type RAG struct {
 	loaders      map[*regexp.Regexp]Loader // this map a regexp as string to a loader
 }
 
-type Fusion struct {
-	RAG
-	llm LLM
-}
-
 func New(index *index.Index) *RAG {
 	rag := &RAG{
 		index:        index,
diff --git a/rag/rag_fusion.go b/rag/rag_fusion.go
index e8363c82..2c55eace 100644
--- a/rag/rag_fusion.go
+++ b/rag/rag_fusion.go
@@ -17,6 +17,11 @@ var ragFusionPrompts = []string{
 	"OUTPUT (4 queries):",
 }
 
+type Fusion struct {
+	RAG
+	llm LLM
+}
+
 func NewFusion(index *index.Index, llm LLM) *Fusion {
 	return &Fusion{
 		RAG: *New(index),
diff --git a/rag/sub_document.go b/rag/sub_document.go
new file mode 100644
index 00000000..b4e0d0f4
--- /dev/null
+++ b/rag/sub_document.go
@@ -0,0 +1,121 @@
+package rag
+
+import (
+	"context"
+	"regexp"
+
+	"github.com/henomis/lingoose/document"
+	"github.com/henomis/lingoose/index"
+	"github.com/henomis/lingoose/textsplitter"
+	"github.com/henomis/lingoose/thread"
+	"github.com/henomis/lingoose/types"
+)
+
+const (
+	defaultSubDocumentRAGChunkSize      = 8192
+	defaultSubDocumentRAGChunkOverlap   = 0
+	defaultSubDocumentRAGChildChunkSize = 512
+)
+
+type SubDocumentRAG struct {
+	RAG
+	childChunkSize uint
+	llm            LLM
+}
+
+//nolint:lll
+var SubDocumentRAGSummarizePrompt = "Please give a concise summary of the context in 1-2 sentences.\n\nContext: {{.context}}"
+
+func NewSubDocumentRAG(index *index.Index, llm LLM) *SubDocumentRAG {
+	return &SubDocumentRAG{
+		RAG: *New(index).
+			WithChunkSize(defaultSubDocumentRAGChunkSize).
+			WithChunkOverlap(defaultSubDocumentRAGChunkOverlap),
+		childChunkSize: defaultSubDocumentRAGChildChunkSize,
+		llm:            llm,
+	}
+}
+
+func (r *SubDocumentRAG) WithChunkSize(chunkSize uint) *SubDocumentRAG {
+	r.chunkSize = chunkSize
+	return r
+}
+
+func (r *SubDocumentRAG) WithChildChunkSize(childChunkSize uint) *SubDocumentRAG {
+	r.childChunkSize = childChunkSize
+	return r
+}
+
+func (r *SubDocumentRAG) WithChunkOverlap(chunkOverlap uint) *SubDocumentRAG {
+	r.chunkOverlap = chunkOverlap
+	return r
+}
+
+func (r *SubDocumentRAG) WithTopK(topK uint) *SubDocumentRAG {
+	r.topK = topK
+	return r
+}
+
+func (r *SubDocumentRAG) WithLoader(sourceRegexp *regexp.Regexp, loader Loader) *SubDocumentRAG {
+	r.loaders[sourceRegexp] = loader
+	return r
+}
+
+func (r *SubDocumentRAG) AddSources(ctx context.Context, sources ...string) error {
+	for _, source := range sources {
+		documents, err := r.addSource(ctx, source)
+		if err != nil {
+			return err
+		}
+
+		subDocuments, err := r.generateSubDocuments(ctx, documents)
+		if err != nil {
+			return err
+		}
+
+		err = r.index.LoadFromDocuments(ctx, subDocuments)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (r *SubDocumentRAG) generateSubDocuments(
+	ctx context.Context,
+	documents []document.Document,
+) ([]document.Document, error) {
+	var subDocuments []document.Document
+
+	for _, doc := range documents {
+		t := thread.New().AddMessages(
+			thread.NewUserMessage().AddContent(
+				thread.NewTextContent(SubDocumentRAGSummarizePrompt).Format(
+					types.M{
+						"context": doc.Content,
+					},
+				),
+			),
+		)
+
+		err := r.llm.Generate(ctx, t)
+		if err != nil {
+			return nil, err
+		}
+		summary := t.LastMessage().Contents[0].AsString()
+
+		subChunks := textsplitter.NewRecursiveCharacterTextSplitter(
+			int(r.childChunkSize),
+			0,
+		).SplitDocuments([]document.Document{doc})
+
+		for i := range subChunks {
+			subChunks[i].Content = summary + "\n" + subChunks[i].Content
+		}
+
+		subDocuments = append(subDocuments, subChunks...)
+	}
+
+	return subDocuments, nil
+}