Onsets are obligatory in the most typical syllable found cross‐linguistically, the consonant—vowel (CV) syllable, and as such, are found ubiquitously across languages. This chapter explores various aspects of onsets, covering much of their structural, segmental, and suprasegmental behavior. Using empirical data as a point of departure, various stances and theoretical views will be addressed on a number of issues. These include the presence of the onset in unmarked CV syllables (§1), onset clusters and the role of sonority in their formation (§2), and the structure and representation of the onset within the syllable (§3). The focus will then shift to the onset's often disregarded role in suprasegmental phonology with reference to several weight‐based phenomena (§4). The chapter closes by briefly reviewing approaches that tackle the onset—coda asymmetry (§5).