A captain's responsibilities are wide-ranging in expertise and include navigation, operation of the ship's equipment, business functions, and the assignment and monitoring of duties performed by all crew members. Ensuring all equipment receives proper maintenance and follows environmental regulations also falls under their jurisdiction. Lesser, but equally important to their other duties, is the task of keeping regular logs through the journey, and supervising passenger and crew embarking and disembarking. Nearly everything that happens on the vessel must be rigorously documented and checked by the ship captain to keep a formal record of every excursion and the ship's functions throughout. In the instance of international travel, it is the captain's duty to meet the requirements of local and international customs and inspections.

In some cases, the captain must maintain the ship's financial operations and accounting, including cash-on-hand and payroll, in the absence of a purser on board. They must also be responsible for the ship's security, both in terms of basic operation and under extreme circumstances, such as responding to threats from terrorists, pirates, hijackers, and stowaways.

In the instance of trouble during the voyage that results in cargo damage or loss, improper ship piloting, or the injury or death of a crew member, a captain must act as a direct contact to local authorities to aid in the preceding investigation. They must provide thorough documentation and accounts of the event in question and be capable of providing any further information the investigative party may require.