Forests and grasslands are among the largest biomes on Earth, covering ~31% and ~40% of the world's land surface, respectively. They provide a range of benefits, also known as ecosystem services, of fundamental importance for human well-being and survival. Provisioning, regulation, culture, and support are the four broad categories of services. Biodiversity is the basis of all ecosystem services and is mainly high in tropical regions. However, despite all their importance, both biomes are more severely threatened than ever. Two main factors are associated with their loss and degradation: human activities and climate change. This study explains the importance of forests and grasslands in generating benefits for society, how environmental degradation impacts their ability to provide these benefits, and the science underlying their major ecosystem services and biodiversity.