Cyclin-dependent kinase 11 is a relatively neglected member of the transcriptional CDKs subfamily, despite possibly being the most versatile CDK in this group. Different CDK11 variants are known to play essential roles in major cellular processes as mRNA transcription (CDK11p110), mitosis (CDK11p58), and apoptosis (CDK11p46 and CDK11p60). Each CDK11 species targets a particular set of substrates related to its functional background, but all isoforms originate from the CDC2L gene complex in human chromosome 1p36.2. CDK11p110 is synthesized through regular cap-dependent translation of CDK11 mRNA, whereas CDK11p58 translation is initiated through an IRES, and occurs only at G2 and M phases. CDK11p46 and CDK11p60, in turn, are the products of caspase cleavage of the larger isoforms during apoptosis. L-type cyclins are the main partners of CDK11, although CDK11p58 species interacts specifically with cyclin D3. The link between CDK11 dysfunction and cancer has been known for a long time, and critical roles in the proliferation of different cancer cell lines have been assigned to CDK11. This review summarizes more than 25 years of studies that unraveled CDK11 genetic and functional aspects.