diff --git a/README.md b/README.md
index c9c577c..f1bc184 100644
--- a/README.md
+++ b/README.md
@@ -216,6 +216,61 @@ Octet 1
 `D`: bit 7, 1 si enlevé, 0 sinon  
 `C`: bit 6, 1 si personnage, 0 si année
 
+### Requête d'information pour la programmation de tag
+
+**En-tête**      : `?`  
+**Longueur**     : 0 octets  
+**Description**  : Message **vide** envoyé du logiciel vers l'objet pour
+demander les informations complètes qui permettront de programmer les tags.  
+Il attend une réponse de l'objet, décrit dans la catégorie suivante.
+
+### Réponse d'information pour la programmation de tag
+
+**En-tête**      : `!`  
+**Longueur**     : 1 + 5*n octets, n le nombre de figurines présentes (>=0)  
+**Description**  : Message de réponse à la requête d'information pour la programmation
+des tags.  
+Le premier octet est fixé et indique le nombre de figurines présentes, et donc
+le nombre d'entrées dans le message.
+Ensuite, chaque entrée est constituée de l'ID actuel, sur un octet, puis de l'UID
+du tag, sur quatre octets.  
+C'est l'UID qui est utilisé dans la demande de programmation pour sélectionner le tag.
+
+#### Schéma
+
+```
+   │Optional, N records
+ ┌─┼────┬──┬────┬──┐
+ │N│UID1│I1│UID2│I2│...
+ └─┴────┴──┴────┴──┘
+ 0 1    5  6    10 11 - Octets
+```
+`N`    : Nombre de tags présents, 1 octet  
+`UIDn` : UID du tag n, 4 octets  
+`In`   : ID du tag n, 1 octet  
+
+### Message de programmation de tag
+
+**En-tête**      : `=`  
+**Longueur**     : 5 octets  
+**Description**  : Message envoyé par le logiciel à l'objet, permet de changer
+(programmer) l'ID stocké dans un tag.  
+Le contenu est formaté de façon similaire à la réponse d'information :
+l'UID du tag à programmer, sur quatre octets, puis le nouvel identifiant du tag,
+sur un octet.  
+On ne programme qu'un tag à la fois.
+
+#### Schéma
+
+```
+ ┌─────┬────┐
+ │ UID │ ID │
+ └─────┴────┘
+ 0     4    5 - Octets
+```
+`UID` : UID du tag à programmer, 4 octets  
+`ID`  : Nouvel ID à programmer, 1 octet  
+
 ### Message informatif
 
 **En-tête**      : `#`  
diff --git a/include/Com.h b/include/Com.h
index 8165ebe..ac3a688 100644
--- a/include/Com.h
+++ b/include/Com.h
@@ -13,8 +13,43 @@
  * functions for the fixed protocols.
  */
 namespace Com {
+	enum ReceivedMessage {
+		NO_MESSAGE,
+		TAG_INFO_REQUEST,
+		TAG_PROGRAMMING,
+		INVALID_MESSAGE,
+	};
+
+	/**
+	 * Struct used for tag info responses and tag programming.
+	 * Would be 8 bytes if not packed due to padding.
+	 */
+	struct __attribute__((packed)) TagInfoRecord {
+		uint32_t uid;
+		uint8_t figId;
+	};
+
 	void sendFigUpdate(int8_t event);
 	void sendComment(const char message[62], ...);
+	/**
+	 * Send the response to the tag info request.
+	 * The TagInfoRecord buffer needs to be properly filled through getTagRecords().
+	 * @param tagCount The amount of tags that are present in the response.
+	 */
+	void sendTagInfo(uint8_t tagCount);
+
+	/**
+	 * @return Pointer to a buffer of TagInfoRecords
+	 */
+	TagInfoRecord* getTagRecords();
+
+	/**
+	 * Check for any incoming message and handle it if needed, returning the
+	 * kind of message received if known, no message if there was nothing to read
+	 * and invalid message otherwise.
+	 * @return Kind of message received.
+	 */
+	ReceivedMessage receiveMessage();
 }
 
 #endif //JIN_BARBAPAPA_COM_H
diff --git a/include/RFID.h b/include/RFID.h
index ef5b02b..66a42f8 100644
--- a/include/RFID.h
+++ b/include/RFID.h
@@ -15,6 +15,7 @@
 #include <MFRC522DriverPinSimple.h>
 #include <MFRC522DriverSPI.h>
 
+#include "Com.h"
 #include "IDs.h"
 #include "Pinout.h"
 
@@ -30,6 +31,8 @@ struct uidNode {
 
 class RFID {
 public:
+	static constexpr int maxTags = 2;
+
 	/***
 	 * Use the main SPI port and NFC chip select by default, but allow choosing
 	 * an alternate chip select and/or SPI bus if needed to allow multiple
@@ -48,11 +51,26 @@ public:
 	 * @return 0 if no change, ID if new tag detected, ID & sign bit if the tag left.
 	 */
 	int8_t checkTags();
+
+	/***
+	 * Populate an already allocated array of sufficient size to fit
+	 * maxTags number of TagInfoRecords.
+	 * @param tagData Pointer to an array of size maxTags*sizeof(Com::TagInfoRecord)
+	 * @return Number of tags actually put in the array.
+	 */
+	uint8_t gatherTagInfo(Com::TagInfoRecord* tagData);
+
+	/***
+	 * Change the ID stored in a tag so that it matches tagToProgram.
+	 * @param tagToProgram Pointer to an existing struct with the data to program.
+	 * @return True if the programming succeeded.
+	 */
+	bool programTag(Com::TagInfoRecord* tagToProgram);
 private:
+	static const byte tagIdBlock = 0x11;
 	/* Used for "encrypted" communication with the tags. */
 	static MFRC522Constants::MIFARE_Key defaultKey;
-	static constexpr int maxTags = 2;
-	int currentActiveTags = 0;
+	static int currentActiveTags;
 
 	/*
 	 * The linked list tracking active tags.
@@ -90,11 +108,22 @@ private:
 	/**
 	 * Read block at blockADdr from tagUid and return if the read succeeded or not.
 	 * The read block will be in comData.
+	 * The tag needs to be already woken up.
 	 * @param tagUid Uid of the tag to be read.
 	 * @param blockAddr Address of the block to be read.
 	 * @return True if read succeeded, false otherwise.
 	 */
 	bool readBlock(MFRC522Constants::Uid &tagUid, byte blockAddr);
+
+	/**
+	 * Write data to tagUid at blockAddr and return if the write succeeded or not.
+	 * The tag needs to be already woken up.
+	 * @param tagUid Uid of the tag to write to.
+	 * @param blockAddr Address of the block to write to.
+	 * @param data Byte to write.
+	 * @return True if write succeeded, false otherwise.
+	 */
+	bool writeBlock(MFRC522Constants::Uid &tagUid, byte blockAddr, uint8_t data);
 };
 
 #endif //JIN_BARBAPAPA_RFID_H
diff --git a/src/Com.cpp b/src/Com.cpp
index adafc82..8c45eaa 100644
--- a/src/Com.cpp
+++ b/src/Com.cpp
@@ -3,9 +3,12 @@
 //
 
 #include "Com.h"
+#include "RFID.h"
 
 namespace Com {
 	byte buffer[64];
+	TagInfoRecord records[RFID::maxTags] = {};
+
 	/**
  	 * Will flush buffer through either HID or Serial depending on build
  	 * options.
@@ -19,7 +22,7 @@ namespace Com {
 		Serial.write((const char*)buffer);
 #endif
 		/* Clear the buffer. */
-		memset(buffer, 0, 64);
+		memset(buffer, 0, sizeof(buffer));
 	}
 
 	void sendFigUpdate(int8_t event) {
@@ -36,4 +39,58 @@ namespace Com {
 		va_end(args);
 		flushBuffer();
 	}
+
+	void sendTagInfo(uint8_t tagCount) {
+		buffer[0] = '!';
+		buffer[1] = tagCount;
+		memcpy(buffer + 2, records, sizeof(TagInfoRecord)*tagCount);
+		flushBuffer();
+	}
+
+	TagInfoRecord* getTagRecords() {
+		return records;
+	}
+
+	inline bool dataAvailable() {
+#ifdef USB_RAWHID
+		return usb_rawhid_available();
+#else
+		/* Serial is used for debug, do not care about message length. */
+		return Serial.available();
+#endif
+	}
+
+	inline void receiveData() {
+		memset(buffer, 0, sizeof(buffer));
+#ifdef USB_RAWHID
+		/* We know we have data, don't need to set a timeout. */
+		usb_rawhid_recv(buffer, 0);
+#else
+		/* Could lead to incomplete messages, but should be OK on Teensy. */
+		Serial.readBytes(buffer, Serial.available());
+#endif
+	}
+
+	ReceivedMessage receiveMessage() {
+		if (!dataAvailable())
+			return NO_MESSAGE;
+		receiveData();
+
+		ReceivedMessage messageType;
+		switch (buffer[0]) {
+			case '?':
+				messageType = TAG_INFO_REQUEST;
+				break;
+			case '=':
+				messageType = TAG_PROGRAMMING;
+				/* Make the record available to the rest of the code. */
+				memset(records, 0, sizeof(records));
+				memcpy(records, buffer + 1, sizeof(TagInfoRecord));
+				break;
+			default:
+				messageType = INVALID_MESSAGE;
+				Serial.printf("Invalid header received : %c\n", buffer[0]);
+		}
+		return messageType;
+	}
 }
diff --git a/src/RFID.cpp b/src/RFID.cpp
index 22c69fc..03b40d5 100644
--- a/src/RFID.cpp
+++ b/src/RFID.cpp
@@ -4,7 +4,11 @@
 
 #include "RFID.h"
 
+static_assert(RFID::maxTags * sizeof(Com::TagInfoRecord) <= 62,
+			  "RFID::maxTags too high, protocol cannot support it.\n");
+
 MFRC522Constants::MIFARE_Key RFID::defaultKey = {0xFF,0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
+int RFID::currentActiveTags = 0;
 
 void RFID::init() {
 	// Create and set up a static linked list to manage active tags.
@@ -58,15 +62,47 @@ int8_t RFID::checkTags() {
 		return 0;
 	}
 	// If the read fails, we cannot use this tag anyway so remove it from the list.
-	if (!readBlock(newTag->uid, 0x11) ) {
+	if (!readBlock(newTag->uid, tagIdBlock) ) {
 		removeActiveTag(newTag, nullptr);
 		return 0;
 	}
-	// TODO: ID check ?
+	// Don' t check the ID, otherwise we cannot program the tag.
 	newTag->tag_ID = comData[0];
 	return newTag->tag_ID;
 }
 
+uint8_t RFID::gatherTagInfo(Com::TagInfoRecord *tagData) {
+	int tagCount = 0;
+	for (uidNode* node = activeTags; node; node = node->next) {
+		// The protocol does not support UIDs other than 4 bytes, so assume it
+		// is the case here directly.
+		tagData[tagCount].uid = *(uint32_t*)(node->uid.uidByte);
+		tagData[tagCount].figId = node->tag_ID;
+		tagCount++;
+	}
+	return tagCount;
+}
+
+bool RFID::programTag(Com::TagInfoRecord *tagToProgram) {
+
+	byte comSize = sizeof(comData);
+
+	mfrc.uid.size = 4;
+	*(uint32_t*)(mfrc.uid.uidByte) = tagToProgram->uid;
+	mfrc.PICC_WakeupA(comData, &comSize);
+	if (mfrc.PICC_Select(&mfrc.uid, mfrc.uid.size) != MFRC522Constants::STATUS_OK) {
+		Serial.println("Failed to wakeup for programming. Is tag still there ?\n");
+		mfrc.PICC_HaltA();
+		return false;
+	}
+
+	if (!writeBlock(mfrc.uid, tagIdBlock, tagToProgram->figId)) {
+		Serial.println("Failed to program tag.");
+		return false;
+	}
+	return true;
+}
+
 uidNode* RFID::addActiveTag(const MFRC522Constants::Uid &newTag) {
 	if (!nextFreeTagSlot) {
 		return nullptr;
@@ -101,16 +137,40 @@ bool RFID::readBlock(MFRC522Constants::Uid &uidToRead, byte blockAddr) {
 	if (mfrc.PCD_Authenticate(
 			MFRC522Constants::PICC_Command::PICC_CMD_MF_AUTH_KEY_A,
 			blockAddr, (&defaultKey),&uidToRead)!= MFRC522Constants::STATUS_OK) {
-		Serial.println("Failed to authenticate");
+		Serial.println("readBlock: Failed to authenticate");
+		mfrc.PICC_HaltA();
 		return false;
-	} else {
-		byte size = sizeof(comData);
-		mfrc.MIFARE_Read(blockAddr, comData, &size);
-//		Serial.printf("Read block : 0x%lX\n", *(uint32_t *)comData);
 	}
+
+	byte size = sizeof(comData);
+	MFRC522::StatusCode status = mfrc.MIFARE_Read(blockAddr, comData, &size);
+//	Serial.printf("Read block : 0x%lX\n", *(uint32_t *)comData);
 	// Needed otherwise no new communications can happen.
 	mfrc.PCD_StopCrypto1();
 	// No need to keep the tag active.
 	mfrc.PICC_HaltA();
-	return true;
+	return status == MFRC522Constants::STATUS_OK;
+}
+
+bool RFID::writeBlock(MFRC522Constants::Uid &uidToRead, byte blockAddr, uint8_t data) {
+	if (mfrc.PCD_Authenticate(
+			MFRC522Constants::PICC_Command::PICC_CMD_MF_AUTH_KEY_A,
+			blockAddr, (&defaultKey),&uidToRead)!= MFRC522Constants::STATUS_OK) {
+		Serial.println("writeBlock: Failed to authenticate");
+		mfrc.PICC_HaltA();
+		return false;
+	}
+
+	byte size = sizeof(comData);
+	for (byte& bufferByte: comData)
+		bufferByte = 0;
+
+	*comData = data;
+
+	MFRC522::StatusCode status = mfrc.MIFARE_Write(blockAddr, comData, size);
+	// Needed otherwise no new communications can happen.
+	mfrc.PCD_StopCrypto1();
+	// No need to keep the tag active.
+	mfrc.PICC_HaltA();
+	return status == MFRC522Constants::STATUS_OK;
 }
diff --git a/src/main.cpp b/src/main.cpp
index 3b5902f..b281973 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -77,6 +77,16 @@ __attribute__((noreturn)) int main() {
 			}
 		}
 
+		Com::ReceivedMessage message = Com::receiveMessage();
+		if (message == Com::TAG_INFO_REQUEST) {
+			uint8_t tagCount = rfid.gatherTagInfo(Com::getTagRecords());
+			Com::sendTagInfo(tagCount);
+		} else if (message == Com::TAG_PROGRAMMING) {
+			if (!rfid.programTag(Com::getTagRecords())) {
+				Com::sendComment("Tag programming failed.");
+			}
+		}
+
 		/* TODO: Drop delay, WFE+timer interrupt(s) ? */
 		delay(25);
 	}