This paper describes a comprehensive review of 31 quasi or experimental research studies from the past decade on the effect of PhET simulations on students' conceptual understanding of physics. Two questions guided the review: (i) To what extent do PhET simulations enhance students' conceptual understanding of physics? (ii) What are the best ways to use PhET simulations to enhance conceptual understanding of physics? The reviewed literature provides robust evidence that PhET simulations can significantly enhance students' conceptual understanding of physics and can be integrated into many active learning instructional environments. The paper also points out gaps and directions of future research and suggests that educators integrate PhET simulations in physics to create more meaningful learning.