Most visitors who arrive in Cambodia are heading to the Angkor Wat temples as their main destination - so it makes sense that the best time to visit Cambodia is when the temples are at their best.
Weather-wise, the best time to visit Siem Reap and Angkor Wat is between December and February, when temperatures drop into the high 20s and the humidity is low enough to be bearable.
However, these months are part of the cool season, which is also high season in the country - this means higher prices, bigger crowds, and more expensive airfares.
For better prices and slightly smaller crowds, consider arriving in March or early April - while temperatures are rising fast at this time, the rainy season is just starting by then, so you should be able to still enjoy the outdoors.
Phnom Penh has hot and humid weather all year-round, with just a small dip in temperature and humidity dropping to around 70 percent during the cool season.
This is also a good time to visit Koh Rong, Cambodia's best beach destination.
Phnom Penh/Silk Weaving and Ancient Temples
Phnom Penh Cooking Class one day