Planning of marine areas is being developed worldwide to foster sustainable ocean management and governance. Marine spatial planning (MSP) is a process that aims to organize the use of the ocean space, as well as the interactions among human uses (e.g., fisheries, aquaculture, shipping, tourism, renewable energy production) and between users and the marine environment. Over the past 30 years, significant progress has been made by governments in their thinking about MSP. The MSP is currently under development in over 66 countries (44% of the nations with marine waters), encompassing six continents and four ocean basins, and the interest in MSP continues to grow. While most countries are still in the early phase of their MSP initiatives, others have already approved, implemented, or even revised marine spatial plans for many years. Despite its acceptance and use, development and implementation of MSP still faces several conceptual and practical challenges, from political to institutional, social, economic, scientific, and environmental sources. The present chapter provides a review on all these topics by addressing three main questions: what is MSP and why is it needed; what is the global distribution of MSP around the world, together with its state of development by region; and what are some of the most prominent and widespread challenges, present and future, that are linked to the development of MSP?