Northern France plays a central role in the debate around the Lower to Middle Paleolithic boundary since the first elaborations of the chronological timescale of Prehistory. Based the discussion around the discovery of the site of Biache-Saint-Vaast in the 1970’s, the onset of the Middle Paleolithic was pushed beyond the traditional Eemian limit (MIS 5e). Reinforced by other discoveries in the 1980’s and the 1990’s, the rich Saalian record of Northern France allowed for proposing a mosaic model of transition – mainly after A. Tuffreau’s works. Considering lithic industries, this model implied that during the MIS 8-6 period the coexistence of Upper Acheulean assemblages (numerous bifaces with little standardized retouched flakes), “Epi-Acheuléen” assemblages (rare bifaces and various retouched flakes) and Mousterian assemblages (Levalloisian industries). Since the 2000’s, progress in dating methods, the reanalysis of some sites with new views on the sedimentary sequences, the taphonomy, the lithic series as well as discovery of new key-sites like Therdonne or Etricourt-Manancourt provide new insights to our knowledge of this time period. A renewal in research themes has been done at the same time which not only focuses on lithic industries but includes a broader perspective incorporating other behavioural issues. What are the consequences of the new discoveries, studies and reanalysis concerning the previous transition model(s) established for northern France? Is our periodization still relevant considering new data on technological, behavioral and cultural changes ? What does the northern France record tell us about settlement and innovative dynamics compared to neighbouring areas (North-western Europe) and mire distant regions like the Near-East? After presenting a quick historical summary of the previous approaches on the Lower to Middle Paleolithic boundary, we will show that the current Saalian record of northern France is both rich and scarce. It implies some limits but the current record allows us to move forward on some current questions around the onset of the Middle Paleolithic. We will discuss some demographic issues considering low and high densities of humans in the region during the Saalian, taking into account chronoclimatic periods, geomorphological, taphonomic and archaeological data.