Its area is roughly equivalent to that of the US states of Vermont and New Hampshire combined. The country's capital and greatest metropolitan area, Santo Domingo, is located on the southern coast. The country's mainland has four important mountain ranges. With mountain ranges running parallel to each other, the Dominican Republic boasts a number of valleys and plains. In between the Central and Septentrional mountain ranges lies the rich and fertile Cibao valley. This major valley is home to the city of Santiago de los Caballeros and most of the farming areas in the nation.

Four major rivers drain the numerous mountains of the Dominican Republic. The Yaque del Norte is the longest and most important Dominican river. It carries excess water down from the Cibao Valley and empties into Monte Cristi Bay, in the northwest. There are many lakes and coastal lagoons; the largest lake is Lago Enriquillo, a saline lake at 40 m below sea level, the lowest point in the West Indies.

The country is a tropical, maritime nation. Wet season is from May to November, with periodic hurricanes between June and November. Most rain falls in the northern and eastern regions. The average rainfall is 1346 mm, with extremes of 2500 mm in the northeast and 500 mm in the west. The main annual temperature ranges from 21 °C in the mountainous regions to 25 °C on the plains and the coast. The average temperature in Santo Domingo in January is 25 °C and it is 30 °C in July. Nonetheless, the highest mountaintops are covered in pine forests and have temperatures that can go several degrees below freezing during winter nights.