In the past decade the availability of massive spectroscopic datasets has made it possible to detect large samples of double peaked (DP) emission line galaxies. The origin of the double peaks can be associated with rotating nuclear disks, nuclear outlfows or dual nuclei which maybe dual active galactic nuclei (DAGN). Such sources give us the opportunity of studying the inspiral of supermassive black holes (SMBHs) in galaxy merger remnants, and its effect on galaxy star formation as well as the surrounding environments via stellar or AGN outflows. In this presentation I will discuss the different types of DP host galaxies, the nature of the nuclei and their importance for identifying dual AGN. I will also discuss their relation to dual nuclei galaxies and how finding dual nuclei in large datasets can complement the study of DP emission line galaxies.