The Köppen climate classification (1884, revised in 1936 as Köppen-Geiger) is the most widely used system for categorising Earth's climates. It uses monthly mean temperature and precipitation values to divide the planet into five main groups: A (tropical), B (arid), C (warm temperate), D (cold continental), and E (polar), each subdivided by rainfall regime (f=no dry season, s=dry summer, w=dry winter) and summer temperature. Spain presents remarkable climatic diversity within the Köppen system: Csa (hot-summer Mediterranean) dominates the interior and eastern peninsula; Csb (warm-summer Mediterranean) appears in Galicia and the Cantabrian coast; BSk (cold semi-arid) covers the southeast (Almería, Murcia) and parts of the Ebro valley; Cfb (oceanic) characterises Atlantic Spain; and Dfc (cold continental) is found in the high Pyrenees. The Canary Islands add subtropical and desert subtypes. This variety makes Spain one of the most climatically diverse countries in Europe. The Köppen classification remains widely used in climate change studies to track the shifting of climate zones: recent models show arid climates (type B) are expanding across the Mediterranean, while polar climates (type E) are retreating at high latitudes. It is a fundamental tool in agriculture, ecology, bioclimatic architecture, and territorial planning.