The basic technical facts of human cytogenetics and the laboratory methods employed in chromosome research are explained in simple terms. The main variables used to describe chromosome images are defined and discussed. Three discriminant analysis models for chromosome classification are developed: one in which each chromosome is classified in isolation, a modification in which the cell, if normal, contains 2 chromosomes of each of the 23 kinds, and a final one in which the cell is the unit of analysis instead of the chromosome. Suggestions are made to reduce the calculations involved and to take into account missing chromosomes. The problem of detection and classification of aberrative chromosomes is studied, also in relation to multiple cell analysis. Finally four relevant problems are briefly discussed: selection of metaphase spreads, selection of variables, uncertain reference classification and measurement of performance.