Political parties become governments by winning elections having put a manifesto containing policy proposals to voters. But not all policies that a government makes while in power can be found in these documents and regardless of where an idea originated, most go through some development within government prior to implementation.

Policy-making can take a number of forms and depends largely on the potential scope and impact of a policy, how much it will cost (the degree to which the Treasury is involved) and whether it will require changes in primary or secondary legislation. There is some hierarchy: a White Paper may follow a Green Paper, but a Green Paper rarely follows a White one.