1. Water: The most significant agent of erosion. It can erode through rainfall, rivers, oceans, and glaciers.

2. Wind: Especially powerful in arid and semi-arid regions, wind can transport sand and dust, causing abrasion and deflation.

3. Ice: Glaciers, a powerful force, carve out valleys and transport large amounts of rock and sediment.

4. Gravity: Causes mass movements like landslides, rockfalls, and soil creep, transporting material downhill.

It's important to note that these agents often work together, their effects compounding and influencing each other. For instance, water can create channels that wind can then erode further.