diff --git a/README.md b/README.md
index d58f51b..de90a04 100644
--- a/README.md
+++ b/README.md
@@ -61,7 +61,7 @@
 TODO
 ----
 
- - Message packetisation and reassembly
+ - Partial packet queue transmit
  - Control messages
  - Message- and packet-buffer pools and preallocation
  - C++ API
diff --git a/core.c b/core.c
index 575d14f..0a5a135 100644
--- a/core.c
+++ b/core.c
@@ -24,15 +24,30 @@
 	/* todo: routing */
 };
 
+struct mctp_msg_ctx {
+	uint8_t		src;
+	uint8_t		tag;
+	uint8_t		last_seq;
+	void		*buf;
+	size_t		buf_size;
+	size_t		buf_alloc_size;
+};
+
 struct mctp {
 	/* todo: multiple busses */
 	struct mctp_bus	busses[1];
 
-	struct mctp_pktbuf	txbuf;
+	struct mctp_pktbuf	*tx_queue_head;
+	struct mctp_pktbuf	*tx_queue_tail;
 
 	/* Message RX callback */
 	mctp_rx_fn		message_rx;
 	void			*message_rx_data;
+
+	/* Message reassembly.
+	 * @todo: flexible context count
+	 */
+	struct mctp_msg_ctx	msg_ctxs[16];
 };
 
 #ifndef BUILD_ASSERT
@@ -40,6 +55,10 @@
 	do { (void)sizeof(char[0-(!(x))]); } while (0)
 #endif
 
+#ifndef ARRAY_SIZE
+#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
+#endif
+
 struct mctp_pktbuf *mctp_pktbuf_alloc(uint8_t len)
 {
 	struct mctp_pktbuf *buf;
@@ -110,6 +129,83 @@
 	return 0;
 }
 
+/* Message reassembly */
+static struct mctp_msg_ctx *mctp_msg_ctx_lookup(struct mctp *mctp,
+		uint8_t src, uint8_t tag)
+{
+	unsigned int i;
+
+	/* @todo: better lookup, if we add support for more outstanding
+	 * message contexts */
+	for (i = 0; i < ARRAY_SIZE(mctp->msg_ctxs); i++) {
+		struct mctp_msg_ctx *ctx = &mctp->msg_ctxs[i];
+		if (ctx->src == src && ctx->tag == tag)
+			return ctx;
+	}
+
+	return NULL;
+}
+
+static struct mctp_msg_ctx *mctp_msg_ctx_create(struct mctp *mctp,
+		uint8_t src, uint8_t tag)
+{
+	struct mctp_msg_ctx *ctx;
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(mctp->msg_ctxs); i++) {
+		struct mctp_msg_ctx *tmp = &mctp->msg_ctxs[i];
+		if (!tmp->src) {
+			ctx = tmp;
+			break;
+		}
+	}
+
+	if (!ctx)
+		return NULL;
+
+	ctx->src = src;
+	ctx->tag = tag;
+
+	return ctx;
+}
+
+static void mctp_msg_ctx_drop(struct mctp_msg_ctx *ctx)
+{
+	ctx->src = 0;
+}
+
+static void mctp_msg_ctx_reset(struct mctp_msg_ctx *ctx)
+{
+	ctx->buf_size = 0;
+}
+
+static int mctp_msg_ctx_add_pkt(struct mctp_msg_ctx *ctx,
+		struct mctp_pktbuf *pkt)
+{
+	size_t len;
+
+	len = mctp_pktbuf_size(pkt) - sizeof(struct mctp_hdr);
+
+	if (ctx->buf_size + len > ctx->buf_alloc_size) {
+		size_t new_alloc_size;
+
+		/* @todo: finer-grained allocation, size limits */
+		if (!ctx->buf_alloc_size) {
+			new_alloc_size = 4096;
+		} else {
+			new_alloc_size = ctx->buf_alloc_size * 2;
+		}
+		ctx->buf = __mctp_realloc(ctx->buf, new_alloc_size);
+		ctx->buf_alloc_size = new_alloc_size;
+	}
+
+	memcpy(ctx->buf + ctx->buf_size, mctp_pktbuf_data(pkt), len);
+	ctx->buf_size += len;
+
+	return 0;
+}
+
+/* Core API functions */
 struct mctp *mctp_init(void)
 {
 	struct mctp *mctp;
@@ -147,12 +243,75 @@
 		struct mctp_pktbuf *pkt)
 {
 	struct mctp_bus *bus = &mctp->busses[bus_id];
+	struct mctp_msg_ctx *ctx;
+	struct mctp_hdr *hdr;
+	uint8_t flags, seq, tag;
 	size_t len;
 	void *p;
+	int rc;
 
-	len = pkt->end - pkt->mctp_hdr_off - sizeof(struct mctp_hdr);
-	p = pkt->data + pkt->mctp_hdr_off + sizeof(struct mctp_hdr),
-	mctp->message_rx(bus->eid, mctp->message_rx_data, p, len);
+	hdr = mctp_pktbuf_hdr(pkt);
+
+	if (hdr->dest != bus->eid)
+		/* @todo: non-local packet routing */
+		return;
+
+	flags = hdr->flags_seq_tag & (MCTP_HDR_FLAG_SOM | MCTP_HDR_FLAG_EOM);
+	tag = (hdr->flags_seq_tag >> MCTP_HDR_TAG_SHIFT) & MCTP_HDR_TAG_MASK;
+	seq = (hdr->flags_seq_tag >> MCTP_HDR_SEQ_SHIFT) & MCTP_HDR_SEQ_MASK;
+
+	switch (flags) {
+	case MCTP_HDR_FLAG_SOM | MCTP_HDR_FLAG_EOM:
+		/* single-packet message - send straight up to rx function,
+		 * no need to create a message context */
+		len = pkt->end - pkt->mctp_hdr_off - sizeof(struct mctp_hdr);
+		p = pkt->data + pkt->mctp_hdr_off + sizeof(struct mctp_hdr),
+		mctp->message_rx(bus->eid, mctp->message_rx_data, p, len);
+		break;
+
+	case MCTP_HDR_FLAG_SOM:
+		/* start of a new message - start the new context for
+		 * future message reception. If an existing context is
+		 * already present, drop it. */
+		ctx = mctp_msg_ctx_lookup(mctp, hdr->src, tag);
+		if (ctx) {
+			mctp_msg_ctx_reset(ctx);
+		} else {
+			ctx = mctp_msg_ctx_create(mctp, hdr->src, tag);
+			if (((ctx->last_seq + 1) % 4) != seq) {
+				mctp_msg_ctx_drop(ctx);
+				return;
+			}
+		}
+
+		rc = mctp_msg_ctx_add_pkt(ctx, pkt);
+		if (rc) {
+			mctp_msg_ctx_drop(ctx);
+		} else {
+			ctx->last_seq = seq;
+		}
+
+		break;
+
+	case MCTP_HDR_FLAG_EOM:
+		ctx = mctp_msg_ctx_lookup(mctp, hdr->src, tag);
+		if (!ctx)
+			return;
+
+		if (((ctx->last_seq + 1) % 4) != seq) {
+			mctp_msg_ctx_drop(ctx);
+			return;
+		}
+
+		rc = mctp_msg_ctx_add_pkt(ctx, pkt);
+		if (!rc) {
+			mctp->message_rx(bus->eid, mctp->message_rx_data,
+					ctx->buf, ctx->buf_size);
+		}
+
+		mctp_msg_ctx_drop(ctx);
+		break;
+	}
 }
 
 static int mctp_packet_tx(struct mctp *mctp __attribute__((unused)),
@@ -165,33 +324,56 @@
 int mctp_message_tx(struct mctp *mctp, mctp_eid_t eid,
 		void *msg, size_t msg_len)
 {
-	struct mctp_pktbuf *pkt;
+	struct mctp_pktbuf *pkt, *tmp;
 	struct mctp_hdr *hdr;
 	struct mctp_bus *bus;
-	int rc;
-
-	/* todo: multiple-packet messages, sequence numbers */
-	assert(msg_len <= MCTP_MTU);
+	size_t pkt_len, p;
 
 	bus = find_bus_for_eid(mctp, eid);
 
-	pkt = mctp_pktbuf_alloc(msg_len + sizeof(*hdr));
-	hdr = mctp_pktbuf_hdr(pkt);
+	/* queue up packets, each of max MCTP_MTU size */
+	for (p = 0; p < msg_len; ) {
+		pkt_len = msg_len - p;
+		if (pkt_len > MCTP_MTU)
+			pkt_len = MCTP_MTU;
 
-	/* todo: tags */
-	hdr->ver = bus->binding->version & 0xf;
-	hdr->dest = eid;
-	hdr->src = bus->eid;
-	hdr->flags_seq_tag = MCTP_HDR_FLAG_SOM |
-		MCTP_HDR_FLAG_EOM |
-		(0 << MCTP_HDR_SEQ_SHIFT) |
-		MCTP_HDR_FLAG_TO |
-		(0 << MCTP_HDR_TAG_SHIFT);
+		pkt = mctp_pktbuf_alloc(pkt_len + sizeof(*hdr));
+		hdr = mctp_pktbuf_hdr(pkt);
 
-	/* todo: zero copy? */
-	memcpy(mctp_pktbuf_data(pkt), msg, msg_len);
+		/* todo: tags */
+		hdr->ver = bus->binding->version & 0xf;
+		hdr->dest = eid;
+		hdr->src = bus->eid;
+		hdr->flags_seq_tag = MCTP_HDR_FLAG_SOM |
+			MCTP_HDR_FLAG_EOM |
+			(0 << MCTP_HDR_SEQ_SHIFT) |
+			MCTP_HDR_FLAG_TO |
+			(0 << MCTP_HDR_TAG_SHIFT);
 
-	rc = mctp_packet_tx(mctp, bus, pkt);
+		memcpy(mctp_pktbuf_data(pkt), msg + p, pkt_len);
 
-	return rc;
+		/* add to tx queue */
+		if (mctp->tx_queue_tail)
+			mctp->tx_queue_tail->next = pkt;
+		else
+			mctp->tx_queue_head = pkt;
+		mctp->tx_queue_tail = pkt;
+
+		p += pkt_len;
+	}
+
+	/* send queued packets */
+	for (pkt = mctp->tx_queue_head; pkt;) {
+		mctp_prdebug("sending pkt, len %d",
+				mctp_pktbuf_size(pkt));
+		mctp_packet_tx(mctp, bus, pkt);
+		tmp = pkt->next;
+		mctp_pktbuf_free(pkt);
+		pkt = tmp;
+	}
+
+	mctp->tx_queue_tail = NULL;
+	mctp->tx_queue_head = NULL;
+
+	return 0;
 }