What is the difference between a Convention and a protocol ?

Convention

A convention is formal agreement between states and is usually an instrument negotiated under an international organisation.

For example, shipping has many conventions that were negotiated under International Maritime organisation (IMO). Some of these are

  • International convention on safety of life at sea (SOLAS)
  • International convention for prevention of pollution at sea (MARPOL)
  • International convention on Load Lines
  • International convention on Tonnage measurement of ships
  • International convention on the control of harmful anti fouling system on ships

Protocol

A protocol is one of the ways in which a convention can be modified.

A protocol is used for the modification of an IMO convention when 

  • There is a significant change to the original convention
  • When a new chapter is added to the original convention. For example when Annex VI was added to the MARPOL
  • When a change is applicable to the all the chapters
  • When IMO feels, the change need to be brought by the protocol

The amendments by protocols are not binding on all the states that have ratified the original convention. The amendments by the protocols are only binding to the states that ratify the new protocol.

For example IMO introduced "harmonised system for ship certification". But this change required change in the protocol of the SOLAS 74. So IMO had to bring these changes by a new protocol to the SOLAS called 1988 protocol to the SOLAS.

Now all the states that had ratified the SOLAS 74 will not become party to this new protocol. So they may or may not choose to be part of this protocol.