diff --git a/zebra-chain/src/block.rs b/zebra-chain/src/block.rs
index 1c26afdfe..d0c45dcd9 100644
--- a/zebra-chain/src/block.rs
+++ b/zebra-chain/src/block.rs
@@ -1,26 +1,62 @@
 //! Definitions of block datastructures.
 
-use crate::transaction::Transaction;
 use chrono::{DateTime, Utc};
+use std::io;
+
+use crate::merkle_tree::MerkleTree;
+use crate::serialization::{SerializationError, ZcashDeserialize, ZcashSerialize};
+use crate::sha256d_writer::Sha256dWriter;
+use crate::transaction::Transaction;
+
+/// A SHA-256d hash of a BlockHeader.
+///
+/// This is useful when one block header is pointing to its parent
+/// block header in the block chain. ⛓️
+pub struct BlockHash([u8; 32]);
+
+impl From<BlockHeader> for BlockHash {
+    fn from(block_header: BlockHeader) -> Self {
+        let mut hash_writer = Sha256dWriter::default();
+        block_header
+            .zcash_serialize(&mut hash_writer)
+            .expect("Block headers must serialize.");
+        Self(hash_writer.finish())
+    }
+}
+
+/// A SHA-256d hash of the root node of a merkle tree of SHA256-d
+/// hashed transactions in a block.
+pub struct MerkleRootHash([u8; 32]);
+
+impl From<MerkleTree<Transaction>> for MerkleRootHash {
+    fn from(merkle_tree: MerkleTree<Transaction>) -> Self {
+        let mut hash_writer = Sha256dWriter::default();
+        merkle_tree
+            .zcash_serialize(&mut hash_writer)
+            .expect("The merkle tree of transactions must serialize.");
+        Self(hash_writer.finish())
+    }
+}
 
 /// Block header
 pub struct BlockHeader {
     /// A SHA-256d hash in internal byte order of the previous block’s
     /// header. This ensures no previous block can be changed without
     /// also changing this block’s header .
-    previous_block_hash: [u8; 32],
+    previous_block_hash: BlockHash,
 
     /// A SHA-256d hash in internal byte order. The merkle root is
-    /// derived from the hashes of all transactions included in this
-    /// block, ensuring that none of those transactions can be modied
-    /// without modifying the header.
+    /// derived from the SHA256d hashes of all transactions included
+    /// in this block as assembled in a binary tree, ensuring that
+    /// none of those transactions can be modied without modifying the
+    /// header.
     merkle_root_hash: [u8; 32],
 
     /// [Sapling onward] The root LEBS2OSP256(rt) of the Sapling note
     /// commitment tree corresponding to the nal Sapling treestate of
     /// this block.
     // TODO: replace type with custom SaplingRoot or similar type
-    // hash_final_sapling_root: [u8; 32],
+    // hash_final_sapling_root: SaplingRootHash,
 
     /// The block timestamp is a Unix epoch time (UTC) when the miner
     /// started hashing the header (according to the miner).
@@ -55,12 +91,24 @@ impl BlockHeader {
     }
 }
 
+impl ZcashSerialize for BlockHeader {
+    fn zcash_serialize<W: io::Write>(&self, writer: W) -> Result<(), SerializationError> {
+        unimplemented!();
+    }
+}
+
+impl ZcashDeserialize for BlockHeader {
+    fn zcash_deserialize<R: io::Read>(reader: R) -> Result<Self, SerializationError> {
+        unimplemented!();
+    }
+}
+
 /// A block in your blockchain.
 pub struct Block {
     /// First 80 bytes of the block as defined by the encoding used by
-    /// "block" messages
+    /// "block" messages.
     pub header: BlockHeader,
 
-    ///
+    /// Block transactions.
     pub transactions: Vec<Transaction>,
 }
diff --git a/zebra-chain/src/lib.rs b/zebra-chain/src/lib.rs
index c945b00e1..710d09934 100644
--- a/zebra-chain/src/lib.rs
+++ b/zebra-chain/src/lib.rs
@@ -4,6 +4,9 @@
 #[macro_use]
 extern crate failure;
 
+mod merkle_tree;
+mod sha256d_writer;
+
 pub mod block;
 pub mod serialization;
 pub mod transaction;
diff --git a/zebra-chain/src/merkle_tree.rs b/zebra-chain/src/merkle_tree.rs
new file mode 100644
index 000000000..bc828f517
--- /dev/null
+++ b/zebra-chain/src/merkle_tree.rs
@@ -0,0 +1,34 @@
+//! A binary hash tree of SHA256d (two rounds of SHA256) hashes for
+//! node values.
+
+use std::io;
+use std::io::prelude::*;
+
+use sha2::{Digest, Sha256};
+
+use crate::serialization::{SerializationError, ZcashDeserialize, ZcashSerialize};
+
+/// A binary hash tree of SHA256d (two rounds of SHA256) hashes for
+/// node values.
+#[derive(Default)]
+pub struct MerkleTree<T> {
+    leaves: Vec<T>,
+}
+
+impl<T> MerkleTree<T> {
+    pub fn get_root(&self) -> Sha256 {
+        unimplemented!();
+    }
+}
+
+impl<T> ZcashSerialize for MerkleTree<T> {
+    fn zcash_serialize<W: io::Write>(&self, writer: W) -> Result<(), SerializationError> {
+        unimplemented!();
+    }
+}
+
+impl<T> ZcashDeserialize for MerkleTree<T> {
+    fn zcash_deserialize<R: io::Read>(reader: R) -> Result<Self, SerializationError> {
+        unimplemented!();
+    }
+}
diff --git a/zebra-chain/src/sha256d_writer.rs b/zebra-chain/src/sha256d_writer.rs
new file mode 100644
index 000000000..5e835cdfc
--- /dev/null
+++ b/zebra-chain/src/sha256d_writer.rs
@@ -0,0 +1,33 @@
+//! A Writer for Sha256d-related (two rounds of SHA256) types.
+
+use std::io::prelude::*;
+
+use sha2::{Digest, Sha256};
+
+/// A type that lets you write out SHA256d (double-SHA256, as in two rounds).
+#[derive(Default)]
+pub struct Sha256dWriter {
+    hash: Sha256,
+}
+
+impl Sha256dWriter {
+    /// Consume the Writer and produce the hash result.
+    pub fn finish(self) -> [u8; 32] {
+        let result1 = self.hash.result();
+        let result2 = Sha256::digest(&result1);
+        let mut buffer = [0u8; 32];
+        buffer[0..32].copy_from_slice(&result2[0..32]);
+        buffer
+    }
+}
+
+impl Write for Sha256dWriter {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        self.hash.input(buf);
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
diff --git a/zebra-chain/src/types.rs b/zebra-chain/src/types.rs
index a9a7e8203..43be396c6 100644
--- a/zebra-chain/src/types.rs
+++ b/zebra-chain/src/types.rs
@@ -1,6 +1,6 @@
 //! Newtype wrappers for primitive data types with semantic meaning.
 
-/// A 4-byte checksum using truncated double SHA256.
+/// A 4-byte checksum using truncated double-SHA256 (two rounds of SHA256).
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub struct Sha256dChecksum(pub [u8; 4]);