What is the difference between ReAct and Plan-and-Execute?

ReAct interleaves thinking and acting at every step, deciding the next action based on the previous observation. Plan-and-Execute first generates a complete multi-step plan, then executes each step in order. ReAct adapts better when results are unexpected, while Plan-and-Execute is more efficient when the path is predictable. Many production agents use Plan-and-Execute at the high level and ReAct within steps.