Extragalactic contributions to the CMB signal

One of the main challenges facing upcoming Cosmic Microwave Background (CMB) experiments aiming at measuring temperature anisotropies with great accuracy will be to assess the contamination of CMB measurements by galactic and extragalactic foregrounds. On the extragalactic side, confusion noise from extragalactic sources hampers the detection of intrinsic CMB anisotropies at small angular scales. Secondary CMB anisotropies must also be carefully accounted for in order to isolate the primordial fluctuations. We present in this article a brief overview of the extragalactic contributions to the CMB. The galactic foregrounds are discussed elsewhere (Giard and Lagache, this issue). To cite this article: G. Lagache, N. Aghanim, C. R. Physique 4 (2003).