This page is a summary only. Freshwater fishing in Scotland is governed by the Salmon and Freshwater Fisheries (Consolidation) (Scotland) Act 2003 and local rules that vary by river district. Always check the official Scottish Government recreational fishing guidance and the local fishery before you fish.
Scotland has no rod licence. Instead, permission is the legal cornerstone:
In practice: always buy a permit or get written permission before fishing.
Since 2016, national salmon conservation regulations grade each river annually into conservation categories, which determine whether salmon can be killed or must be released. See conservation of wild salmon on gov.scot, and the freshwater fisheries licensing collection for consents to catch fish by other means.
The law is the minimum. District salmon fishery boards and individual fisheries set their own rules on methods, catch and release, and seasons — check the rules and permission details on the water's page here, and with the fishery, before fishing.
Fishing elsewhere in Britain? See the bylaws for England and Wales.