With the emergence of behavioural measurement and profile analysis on internet sites, companies now have the opportunity to target various Internet populations on a large diversity of web sites and/or channels of site. Setting up ones online media plan not only means chasing after general public sites with high visibility, but also analysing affinities of target populations with multiple channels and identifying market niches. This paper aims at underlining the great potential of online media planing as compared to other traditional media. It raises the issues of selecting appropriate indicators so as to better target profiles, and choosing appropriate data collection techniques that thus allow a consistent level of analysis. Specific cases of online media plan are used to illustrate the paper.