A new guide published by the Information Commissioner could help members of the public understand how their personal data can be shared between companies and organisations.
Next week, the watchdog will also release a draft good practice guide to help organisations comply with the Data Protection Act when sharing personal information.
The publications come as debate grows over data sharing and privacy concerns.
The government's move last month to give the police access to data on millions of individuals' car journeys gathered by congestion charging cameras sparked controversy - as did prime minister Gordon Brown's inclusion of new data-sharing powers in three planned government bills.
But the debate has also seen calls for greater data sharing between public sector bodies, with the latest call coming from the Commons public administration committee, which highlighted the way sharing information could increase the uptake of council tax benefit.
Iain Bourne, head of data protection projects at the ICO, said: "More and more information is being shared about us, often for useful and wholly legitimate purposes. It is important that individuals are aware of their rights under the Data Protection Act."
The new guidance for the public sets out what people can expect from organisations sharing information about them and explains how to raise concerns.
"Information sharing can often take place without your consent. In many cases where you are not asked to consent the information sharing is reasonable and expected. However, it should be clear why the sharing is taking place and who is involved in it," the guide says.
It cites a number of examples of data sharing involving public sector bodies such as the NHS, police and Department of Work and Pensions - and the private sector example of credit reference agencies.
The ICO has also issued separate guidance aimed at helping local authorities and other organisations handle information about business people in line with the Data Protection Act.