On a day to day basis it is quite difficult to tell if you are being followed, especially if you take the same routes most of the time and lots of other people take those same routes too. If you see the same face though in multiple locations and on more than one day, then it may be that someone has an unhealthy interest in you and you should seek assistance. If possible by using your mobile phone, try and get a photo of the person you think is watching you. If they are in a car then try and get a photo of that too. If someone does have an unhealthy interest in you and you think they are following you outside of your home, then you should seek to acquire whatever evidence that you are safely able to obtain and do not go anywhere were you would be alone. Call for assistance. If you have any fear for your safety, you should call the police, or attend at a police station. If it is a matter of nuisance, record the occurrences that it is happening or consider employing an investigator to conduct a counter-surveillance investigation. A good investigator, if they see you being too observant to their actions, will usually abort the case, or deploy their 2nd agent to take over. No professional investigator will put a target in fear.