diff --git a/blockchain/block.go b/blockchain/block.go
new file mode 100644
index 0000000..11eb130
--- /dev/null
+++ b/blockchain/block.go
@@ -0,0 +1,57 @@
+package blockchain
+
+// BlockHeader contains metadata about a block
+import (
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/gob"
+	"io"
+)
+
+// BlockHeader contains metadata about a block
+type BlockHeader struct {
+	blockNumber uint32
+	lastBlock   Hash
+	miner       Wallet
+}
+
+// Marshal converts a BlockHeader to a byte slice
+func (bh *BlockHeader) Marshal() []byte {
+	buf := []byte{}
+	binary.LittleEndian.PutUint32(buf, bh.blockNumber)
+	for _, b := range bh.lastBlock {
+		buf = append(buf, b)
+	}
+	buf = append(buf, bh.miner.Marshal()...)
+	return buf
+}
+
+// Block represents a block in the blockchain. Contains transactions and header metadata.
+type Block struct {
+	BlockHeader
+	transactions []*Transaction
+}
+
+// Marshal converts a Block to a byte slice
+func (b *Block) Marshal() []byte {
+	buf := b.BlockHeader.Marshal()
+	for _, t := range b.transactions {
+		buf = append(buf, t.Marshal()...)
+	}
+	return buf
+}
+
+// Encode writes the marshalled block to the given io.Writer
+func (b *Block) Encode(w io.Writer) {
+	gob.NewEncoder(w).Encode(b)
+}
+
+// Decode reads the marshalled block from the given io.Reader
+func (b *Block) Decode(r io.Reader) {
+	gob.NewDecoder(r).Decode(b)
+}
+
+// Hash computes and returns the SHA256 hash of the block
+func (b *Block) Hash() Hash {
+	return sha256.Sum256(b.Marshal())
+}
diff --git a/blockchain/blockchain.go b/blockchain/blockchain.go
new file mode 100644
index 0000000..4ce12c7
--- /dev/null
+++ b/blockchain/blockchain.go
@@ -0,0 +1,45 @@
+package blockchain
+
+import (
+	"encoding/gob"
+	"io"
+)
+
+// Hash represents a 256-bit hash of a block or transaction
+type Hash [32]byte
+
+// BlockChain represents a linked list of blocks
+type BlockChain struct {
+	blocks []*Block
+	head   Hash
+}
+
+// Encode writes the marshalled blockchain to the given io.Writer
+func (bc *BlockChain) Encode(w io.Writer) {
+	gob.NewEncoder(w).Encode(bc)
+}
+
+// Decode reads the marshalled blockchain from the given io.Reader
+func (bc *BlockChain) Decode(r io.Reader) {
+	gob.NewDecoder(r).Decode(bc)
+}
+
+// ValidTransaction checks whether a transaction is valid, assuming the blockchain is valid.
+func (bc *BlockChain) ValidTransaction(t *Transaction) bool {
+	// Find the transaction input (I) in the chain (by hash)
+	// Check that output to sender in I is equal to outputs in T
+	// Verify signature of T
+	return false
+}
+
+// ValidBlock checks whether a block is valid
+func (bc *BlockChain) ValidBlock(b *Block) bool {
+	for _, t := range b.transactions {
+		if !bc.ValidTransaction(t) {
+			return false
+		}
+	}
+	// Check that block number is one greater than last block
+	// Check that hash of last block is correct
+	return false
+}
diff --git a/blockchain/transaction.go b/blockchain/transaction.go
new file mode 100644
index 0000000..74a406c
--- /dev/null
+++ b/blockchain/transaction.go
@@ -0,0 +1,71 @@
+package blockchain
+
+import (
+	"crypto/sha256"
+	"encoding/binary"
+)
+
+// TxHashPointer is a reference to a transaction on the blockchain.
+type TxHashPointer struct {
+	blockNumber uint32
+	hash        Hash
+}
+
+// Marshal converts a TxHashPointer to a byte slice
+func (thp TxHashPointer) Marshal() []byte {
+	buf := []byte{}
+	binary.LittleEndian.PutUint32(buf, thp.blockNumber)
+	for _, b := range thp.hash {
+		buf = append(buf, b)
+	}
+	return buf
+}
+
+// TxOutput defines an output to a transaction
+type TxOutput struct {
+	amount    uint64
+	recipient Wallet
+}
+
+// Marshal converts a TxOutput to a byte slice
+func (to TxOutput) Marshal() []byte {
+	buf := []byte{}
+	binary.LittleEndian.PutUint64(buf, to.amount)
+	buf = append(buf, to.recipient.Marshal()...)
+	return buf
+}
+
+// TxBody contains all relevant information about a transaction
+type TxBody struct {
+	sender  Wallet
+	input   TxHashPointer
+	outputs []TxOutput
+}
+
+// Marshal converts a TxBody to a byte slice
+func (tb TxBody) Marshal() []byte {
+	buf := tb.sender.Marshal()
+	buf = append(buf, tb.input.Marshal()...)
+	for _, out := range tb.outputs {
+		buf = append(buf, out.Marshal()...)
+	}
+	return buf
+}
+
+// Transaction contains a TxBody and a signature verifying it
+type Transaction struct {
+	TxBody
+	sig Signature
+}
+
+// Marshal converts a Transaction to a byte slice
+func (t *Transaction) Marshal() []byte {
+	buf := t.TxBody.Marshal()
+	buf = append(buf, t.sig.Marshal()...)
+	return buf
+}
+
+// Hash returns the SHA256 hash of a transaction
+func (t *Transaction) Hash() Hash {
+	return sha256.Sum256(t.Marshal())
+}
diff --git a/blockchain/wallet.go b/blockchain/wallet.go
new file mode 100644
index 0000000..b99bfca
--- /dev/null
+++ b/blockchain/wallet.go
@@ -0,0 +1,51 @@
+package blockchain
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"fmt"
+	"math/big"
+)
+
+// The curve we use for our ECC crypto.
+var curve = elliptic.P256()
+
+// Wallet represents a Cumulus wallet address in the blockchain.
+type Wallet ecdsa.PublicKey
+
+// Signature represents a signature of a transaction.
+type Signature struct {
+	X big.Int
+	Y big.Int
+}
+
+// Marshal converts a signature to a byte slice
+func (s *Signature) Marshal() []byte {
+	return append(s.X.Bytes(), s.Y.Bytes()...)
+}
+
+// New creates a new Wallet backed by a ECC key pair. Uses system entropy.
+func newWallet() (*Wallet, error) {
+	k, err := ecdsa.GenerateKey(curve, rand.Reader)
+	if err != nil {
+		return nil, err
+	}
+	pk := Wallet(k.PublicKey)
+	return &pk, nil
+}
+
+// String returns a human-readable string representation of a wallet
+func (w *Wallet) String() string {
+	return fmt.Sprintf("%x-%x", w.X, w.Y)
+}
+
+// Marshal converts the Wallet to a byte slice
+func (w *Wallet) Marshal() []byte {
+	return elliptic.Marshal(curve, w.X, w.Y)
+}
+
+// Equals checks whether two wallets are the same.
+func (w *Wallet) Equals(other *Wallet) bool {
+	return w.X.Cmp(other.X) == 0 && w.Y.Cmp(other.Y) == 0
+}