The TNM Classification of Malignant Tumours (TNM) is a notation system that describes the stage of a cancer which originates from a solid tumour with alphanumeric codes.

T describes the size of the original (primary) tumour and whether it has invaded nearby tissue, N describes nearby (regional) lymph nodes that are involved, M describes distant metastasis (spread of cancer from one part of the body to another).

The TNM staging system for all solid tumours was devised by Pierre Denoix between 1943 and 1952, using the size and extension of the primary tumor, its lymphatic involvement, and the presence of metastases to classify the progression of cancer it is a classification of the anatomical extent of disease. It has gained wide international acceptance for many solid tumour cancers, but is not applicable to leukaemia and tumours of the central nervous system (CNS).

TNM is developed and maintained by the Union for International Cancer Control (UICC) to achieve consensus on one globally recognised standard for classifying the extent of spread of cancer. The TNM classification is also used by the American Joint Committee on Cancer (AJCC) and the International Federation of Gynecology and Obstetrics (FIGO). In 1987, the UICC and AJCC staging systems were unified into a single staging system.