All governments need to have strict rules to control immigration into their country, which is why immigration law is so important. It refers to the type of control imposed, and also the nature of it.
Closely linked to nationality law, immigration law varies around the world, with some countries having very strict controls imposed whilst others are more relaxed. International law helps to regulate the immigration laws of countries around the world.
Asylum is a big issue within immigration law, due to the human rights issues involved. This is when immigrants need to prove they cannot return to their home-country as they fear persecution. In most countries there is a specified process required to gain asylum. For example, in the UK you must attend an interview and a screening after you declare your intent to claim asylum. You must then wait for the verdict on whether you have been granted asylum, or will be deported.
In terms of letting people visit their country, there are many issues for nations to decide on. Who can visit, when, how long for and what rights they have are just some of the main factors to be evaluated. Generally, most countries are quite relaxed about the nationality of the person visiting, but there are a select few where it is more difficult to enter depending on your nationality.
When entering a country, there are normally customs set up at the entry points. This is where travel documents, such as a passport, are inspected.