diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index cfae4e9fbb..23eb0b5ee5 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -4,10 +4,8 @@
 
 - [Terminology](terminology.md)
 
-- [Synchronization](synchronization.md)
-  - [Introduction to VDFs](vdf.md)
-  - [Proof of History](poh.md)
-  - [Leader Rotation](leader-scheduler.md)
+- [On-chain programs](programs.md)
+  - [The Runtime](runtime.md)
 
 - [Fullnode](fullnode.md)
   - [Tpu](tpu.md)
@@ -15,12 +13,13 @@
   - [Ncp](ncp.md)
   - [JsonRpcService](jsonrpc-service.md)
 
-- [Avalanche replication](avalanche.md)
-  - [Storage](storage.md)
-
-- [On-chain programs](programs.md)
-  - [The Runtime](runtime.md)
-  - [Ledger format](ledger.md)
+- [A Solana Cluster](cluster.md)
+  - [Synchronization](synchronization.md)
+    - [Introduction to VDFs](vdf.md)
+    - [Proof of History](poh.md)
+  - [Ledger Broadcasting](avalanche.md)
+  - [Ledger Replication](storage.md)
+  - [Leader Rotation](leader-scheduler.md)
 
 ## Appendix
 
diff --git a/src/avalanche.md b/src/avalanche.md
index 7c23bc545a..73d3c5b5cc 100644
--- a/src/avalanche.md
+++ b/src/avalanche.md
@@ -1,4 +1,4 @@
-# Avalanche replication
+# Ledger Broadcasting
 
 The [Avalance explainer video](https://www.youtube.com/watch?v=qt_gDRXHrHQ) is
 a conceptual overview of how a Solana leader can continuously process a gigabit
diff --git a/src/cluster.md b/src/cluster.md
new file mode 100644
index 0000000000..bf8ef3bc41
--- /dev/null
+++ b/src/cluster.md
@@ -0,0 +1,10 @@
+# A Solana Cluster
+
+A Solana cluster is a set of fullnodes working together to serve client
+transactions and maintain the integrity of the ledger. Many clusters may
+coexist.  When two clusters share a common genesis block, they attempt to
+converge. Otherwise, they simply ignore the existence of the other.
+Transactions sent to the wrong one are quietly rejected. In this chapter,
+we'll discuss how a cluster is created, how nodes join the cluster, how
+they share the ledger, how they ensure the ledger is replicated, and how
+the cope with buggy and malicious nodes.
diff --git a/src/ledger.md b/src/ledger.md
deleted file mode 100644
index a24627dfc1..0000000000
--- a/src/ledger.md
+++ /dev/null
@@ -1 +0,0 @@
-# Ledger format
diff --git a/src/storage.md b/src/storage.md
index fa969bf20d..9340d3accb 100644
--- a/src/storage.md
+++ b/src/storage.md
@@ -1,4 +1,4 @@
-# Storage
+# Ledger Replication
 
 ## Background