Covalent DNA modifications have been found in numerous organisms and more are continually being discovered and characterized, as detection methods improve. Many of these modifications can affect the conformation of the DNA double helix, often resulting in downstream effects upon transcription factor binding. Some of these modifications have been demonstrated to be stable, while others are viewed as merely transient. DNAmod catalogues information on known DNA modifications, of which the well-known 5-methylcytosine is only one. It aims to profile modifications' properties, building upon data contained within the Chemical Entities of Biological Interest (ChEBI) database. It also provides literature citations and includes curated annotations on mapping techniques and natural occurrence information.