Forty-two families of terrestrial molluscs inhabit Mexico with approx. 1,178 species and subspecies. The most diverse families are the Urocoptidae (265 species), Spiraxidae (246), Bulimulidae (140), Helicinidae (72), Polygyridae (65), Xanthonychidae (58), Humboldtianidae (49), and Pupillidae (47). The 34 medium and small families comprise about 81% of the total number of families; however, their species total only 236 or 20% of the Mexican species. When looking at their distribution, we noticed that, in general, families cover large areas, but while some species are also found in the United States and Central America, the majority seems to be endemic to Mexico. However, our knowledge of the distribution of terrestrial molluscs throughout Mexico may be incomplete because of a lack of systematic collecting in many regions, particularly in the States of Aguascalientes and Tlaxcala.