Lymphoproliferative disorders can be broadly classified into immature neoplasms (acute leukemia), mature B cell tumors and mature T cell tumors. Within these groups are an array of subtypes that arise from cells in different stages of development and with different functions. For example, CD4+ peripheral T cell lymphoma in dogs arises from a T cell that has not yet been activated by antigen and is recently emigrated from the thymus. By contrast, T zone lymphoma appears to be derived from a previously activated T cell and has a transcriptome most closely associated with effector T cells. In people, diffuse large B cell lymphoma can be subdivided into two clinically discrete subtypes by transcriptome profiling, and four clinically discrete subtypes by mutational analysis—each subtype is thought to arise from B cells in different phases of the germinal center/post germinal center reaction. Although most canine and human lymphomas are currently treated with broadly active cytotoxic therapies, as our understanding of the unique pathways, mutational features and antigen expression in different subtypes increases, the possibility of using more targeted therapies becomes more realistic. Both dogs and people can benefit from the use of dogs as a pre-clinical model for experimental therapies, and therefore it is important to identify where human and canine subtypes are similar and where they differ. In this session, classification, dysregulated pathways and the cell of origin of canine lymphoma/leukemia subtypes will be discussed, with an emphasis on similarities and differences with their human counterparts.