Archeops is a balloon--borne experiment dedicated to the measurement of the temperature anisotropies of the cosmic microwave background (CMB) from large angular scales to about 10 arcminutes. A brief introduction to the CMB is given below, followed by a description of the Archeops experiment. Archeops flew on the 7th of February 2002 in the Arctic night from Kiruna (Sweden) to Russia. The analysis of part of these data is described below with the results on the $C_\ell$ spectrum, showing for the first time a continuous link between the large scales and the first acoustic peak. We end up with constraints on the cosmological parameters. We confirm the flatness of the Universe. And, combining the Archeops data with other CMB experiments data and with the HST measurement of $H_0$, we measure for the first time $\Omega_{\Lambda}$ independently of SuperNovae based results.