An analysis of inter-sector employee mobility tables for the 1968-1998 period produces a topography of busi-ness sectors showing energy, transport and construction to be standing on their own, with mobility flows extremely low between these three sectors and the other sectors. The other sectors fall into three distinct groups: a «service group», a «consumer goods group» and a «heavy industry group». Mobility is intense within these groups, but low or inexistent between them. The core of this topography is remarkably stable over time and remains unchanged regardless of whether it is based on skilled or unskilled employee flows, young or older employee flows. This type of inter-sector mobility flow analysis enhances the labour market segmentation diagnoses. Above all, it demonstrates the labour market's imper-fect fluidity. This segmentation of business sectors echoes many business sector typologies based on manpower management methods. The «groups» of sectors and the isolated sectors can each be attached to «primary» and «secondary» labour market segments. Nevertheless, this segmentation of business sectors makes sub-groups of certain areas of business that are found to be similar by the usual typologies. For all its aggregation, the analysis made implies that occupational or product reasoning governs inter-sector mobility flows. A certain percentage of employee circulation is between similar areas of business: either mobility follows the progress of the products or it is explained by the proximity of occupations in these business areas and takes place via professional markets. Often, due to market constraints on the sectors, but also shared unions and collective labour agreements, these neighbouring activities have similar employee management methods, which rely more on the external markets or on the internal markets where these exist.