The aberrant forms of life, neoplasia and cancer, are discussed under the events at the beginning of neoplasia and under five classes of neoplastic lesions. The lesional classes are: 1) The precursor state; 2) Intermediate lesions; 3) Primary cancer; 4) Metastasis; and 5) Metastasis from metastasis. The events at the beginning are a diverse group of agents and mechanisms that induce the lesions of the precursor state, not cancer. The lesions and events produced by induction are similar regardless of the agent. Thus, there must be similar biological principles and mechanisms operative in different neoplastic systems. The classes of neoplastic lesions and cancer are described and a theory derived therefrom. The theory is: Any perturbation that alters a cell or group of cells and their stroma so that they no longer respond appropriately to the forces of tissue, organ, and organismal maintenance, may induce a neoplastic system. The sequential progression of lesions of the induced neoplastic system is the result of a successive series of flaws in the continuum of reciprocal interactions between a group of cells and their stroma. The flaws, appearing seriatim, produce progressive (self)-disorganization of the lesions and progressive loss of response to the forces of tissue and organ maintenance.