A coast guard or coastguard is a maritime security organization of a particular country. The term embraces wide range of responsibilities in different countries, from being a heavily armed military force with customs and security duties to being a volunteer organization tasked with search and rescue without law enforcement authority. In most countries, a typical coast guard's functions are distinct from those of the navy and the transit police, while in certain countries they have similarities to both.

His Majesty's Coastguard (HMCG) is the section of the Maritime and Coastguard Agency responsible, through the Secretary of State for Transport to Parliament, for the initiation and co-ordination of all maritime search and rescue (SAR) within the UK Maritime Search and Rescue Region. This includes the mobilisation, organisation and tasking of adequate resources to respond to persons either in distress at sea, or to persons at risk of injury or death on the cliffs or shoreline of the United Kingdom. Since 2015 it has also been responsible for land-based search and rescue helicopter operations.