This review summarizes current knowledge concerning the isolation, structural elucidation, biological/pharmacological activities, and total synthesis of halogen-containing secondary metabolites isolated from ascidians of the family Didemnidae. Overall, 81 compounds are presented, displaying great structural diversity and possessing a number of significant biological/pharmacological properties. In addition to the most numerous brominated compounds, chlorinated and iodinated ones were also found. The most prolific genus in regard to the number of published papers and isolated molecules is the genus Didemnum, which was treated separately from the rest of the genera of the ascidian family. The structural complexity of the isolated metabolites prompted a number of synthetic endeavors that not only provided conclusive proof of the structure of the metabolites but also enabled the biological tests and the possible application of these metabolites.