Spring (April–June)
The best time to visit. Temperatures are mild, the countryside is green, and the tourist crowds haven't reached their peak. Prague in May is particularly good — the city comes alive, outdoor seating fills up, and the Prague Spring music festival runs through late May and early June. Expect some rain.
Summer (July–August)
Prague gets very crowded and prices reflect it. The city is still wonderful but the Old Town can feel overrun, especially in peak season. Away from Prague, summer is excellent — hiking in Bohemian Switzerland or the Šumava forest, cycling in South Moravia, or just wandering smaller towns that tourists haven't fully discovered. Days are long and warm.
Autumn (September–October)
Another good window. Crowds thin out, the light is beautiful, and South Moravia's wine harvest (vinobraní) festivals run through September and October. Forests turn golden. Temperatures stay pleasant into October.
Winter (November–March)
Cold and often grey, but Prague's Christmas markets (late November through December) are among the best in Europe and draw big crowds. Skiing is possible in the Krkonoše mountains (Giant Mountains) in the north and the Šumava in the south, though the peaks are modest by Alpine standards — better for beginners and families than serious skiers. January and February are quiet and cheap.