A bill is a proposal for a new law or a change to an existing law. A bill can start in the House of Commons or the House of Lords, but it must be approved by both Houses before becoming law.

Legislation is a law that has been passed by parliament. There are two types of legislation, primary and secondary. Primary legislation includes the main laws that are passed by Parliament, such as Acts. Secondary legislation, also known as subordinate legislation, is a law that is created by other bodies or Government Ministers, under the powers of Parliament. Primary and secondary legislation serve different purposes but have the same legislative force. Examples of primary legislation would be the Animals in Scientific Procedures Act which regulates the use of protected animals in scientific procedures, or the Human Medicines Act 1968, which governs the manufacture and supply of medicines for human and veterinary use.

Regulations are a form of secondary legislation which work as a supplement to legislation. For example, when we look at animal testing requirements, they are imposed by regulatory bodies rather than Parliament. Regulations tend to be linked to existing pieces of legislation and help to apply the concepts of legislation to the real world. Examples of regulations would be regulation for the control of chemicals or the Human Medicines Regulations 2012.

In a legislative context, guidelines are recommendations or advice that are provided to illustrate the minimum standards required to be compliant. They are unlikely to be legally binding but may be referred to within legislation. Guidelines are often introduced through harmonisation councils, bodies, or events, where regulators from countries across the world can sign up or implement them. For example, The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) produces guidelines on the development of medicines, including references to animal and non-animal tests, which are implemented by regulatory bodies around the world.  Internationally accepted guidelines standardise product testing making it easier to market products globally. If used effectively they can reduce repeated tests, including animal tests.