diff --git a/TODO.t2t b/TODO.t2t
index 0617834..33914d0 100644
--- a/TODO.t2t
+++ b/TODO.t2t
@@ -21,13 +21,6 @@ Work to do in OwlPS
 - Known bugs:
   - libconfuse bug (Listener & Aggregator): http://bugs.debian.org/639115
 
-- Handle the aggregation format version
-
-  In the aggregation files, a version number describing the file format
-  should be added (as the 2nd field, right after the client's MAC
-  address). That would allow the positioning server to handle several
-  formats instead of just the last version.
-
 - Add a library to parse aggregation files, handling the different
   formats ?
 
diff --git a/libowlps/owlps.h b/libowlps/owlps.h
index 9758440..287729e 100644
--- a/libowlps/owlps.h
+++ b/libowlps/owlps.h
@@ -61,6 +61,12 @@ extern "C" {
 //@}
 
 
+/** @name Miscellaneous informations */
+//@{
+#define OWL_LATEST_AGGREGATION_CSV_FORMAT 1
+//@}
+
+
 /// Directions
 enum owl_directions
 {
diff --git a/owlps-aggregator/owlps-aggregatord.c b/owlps-aggregator/owlps-aggregatord.c
index 311781d..821858b 100644
--- a/owlps-aggregator/owlps-aggregatord.c
+++ b/owlps-aggregator/owlps-aggregatord.c
@@ -1000,6 +1000,9 @@ void output_request(request_list *const request_ptr,
   owl_request_info info;
   request_info_list *request_info_ptr = NULL ;
 
+  // Print CSV format version to the output file
+  fprintf(stream, "%d;", OWL_LATEST_AGGREGATION_CSV_FORMAT) ;
+
   // Print mobile MAC address to the output file
   owl_mac_bytes_to_string_r(request_ptr->mobile_mac_addr_bytes,
                             mac_str) ;
diff --git a/owlps-positioner/inputcsv.cc b/owlps-positioner/inputcsv.cc
index fd2ab55..04e805b 100644
--- a/owlps-positioner/inputcsv.cc
+++ b/owlps-positioner/inputcsv.cc
@@ -44,6 +44,28 @@ bool InputCSV::fill_current_request()
     return false ;
   ++current_line_nb ;
 
+  // Read CSV format version
+  uint_fast16_t csv_format_version ;
+  if (! file.read_field(csv_format_version))
+    {
+      // Wrong number of fields
+      if (Configuration::is_configured("verbose"))
+        cerr << "InputCSV: cannot read the CSV format version.\n" ;
+      return false ;
+    }
+
+  // Check the CSV format
+  switch (csv_format_version)
+    {
+    case 1 :
+      // Format 1 is the only one we handle for now.
+      break ;
+    default :
+      cerr << "InputCSV: CSV format version " << csv_format_version
+           << " is not handled!\n" ;
+      return false ;
+    }
+
   // Read Mobile MAC field
   string mac_mobile ;
   if (! file.read_field(mac_mobile)) // Wrong number of fields
diff --git a/owlps-positioner/inputcsv.hh b/owlps-positioner/inputcsv.hh
index bd17fe5..880e2ef 100644
--- a/owlps-positioner/inputcsv.hh
+++ b/owlps-positioner/inputcsv.hh
@@ -23,8 +23,9 @@
 /// Reads [requests](@ref Request) from a CSV file
 /**
  * CSV format is:
- *   Mobile_MAC;Request_type;Number_of_packets;Timestamp;X;Y;Z;Direction;
- *     AP_MAC_1;Packet_ID_1;SS_1;…;AP_MAC_n;Packet_ID_n;SS_n
+ *     Format_version;Mobile_MAC;Request_type;Number_of_packets;
+ *     Timestamp;X;Y;Z;Direction;AP_MAC_1;Packet_ID_1;SS_1;…;
+ *     AP_MAC_n;Packet_ID_n;SS_n
  */
 class InputCSV: public InputMedium
 {
diff --git a/owlps-positioner/request.cc b/owlps-positioner/request.cc
index 9aa0b84..5e499b0 100644
--- a/owlps-positioner/request.cc
+++ b/owlps-positioner/request.cc
@@ -210,6 +210,12 @@ const string Request::to_csv() const
 {
   ostringstream csv_line ;
 
+  // CSV format version
+  // (this should match OWL_LATEST_AGGREGATION_CSV_FORMAT)
+  constexpr unsigned int aggregation_csv_format = 1 ;
+
+  csv_line << aggregation_csv_format << ';' ;
+
   if (mobile != NULL)
     csv_line << mobile->get_mac_addr() ;