Illegal immigration is travelling to or staying in a country without the approriate documents, entering at an inappropriate place or by an inappropriate method. Usually illegal immigrants try to enter a wealthier country, with a better quality of life, leaving a poorer country behind. There are three main factors which provoke illegal immigration: economic factors, criminal evasion or socio-political environment – effectively anything that can provide enough pressure such that a person is willing to break the law.

In the imagination of many, the mind of an illegal immigrant may seem to be very devious and cunning – while this is not universally true, it is an understandable perception given the tactics that many such desperate people employ. Immigrants have devised more than 30 ways to cross borders illegally. While some try to use more traditional methods, such as presenting falsified documents at the border or crossing border on foot in the middle of a desert, others act like a true inventors. Some immigrants hide themselves inside car seats, some vault over a border fence with a pole, some even try to hide in a suitcase at the airport. According to statistics, chances for the success are very small, because countries, which are primary targets for illegal imigrants, usually conduct serious border control procedures, including constant border patrols and fence building, but these individuals are often desperate, so if there is a way through – they will find it.

Another type of illegal immigration, which does not involve illegal border crossing, is overstaying an otherwise valid visa. In this case immigrants arrive in the host country on a legal basis, but they stay after their visa expires or perform work or other activities that might not be permitted by their visa. This method of illegal immigration requires a lot of effort, since you are forced to evade authorities who might discover your true immigration status. This means you can be scared to involve yourself in any kinds of legal action or participate in any form of legal agreement, this can limit your ability to do such simple things as bank payments, use of credit cards, legal, taxed employment etc. As a result, this approach can be very tiring and mentally exhausting. The legal consequences illegal immigrants who get caught vary from country to country. Usually the measures vary from deportation to jail terms.

Statistics provided by the International Organization for Migration, show that almost 15% of the world's total 214 million immigrants are illegal. For the last few decades the USA has experienced one of the largest influxes of illegal immigrants in human history. The biggest problem being the US–Mexico border, which is used by many thousands of illegal immigrants each year, this in spite of all the measures taken by the US government. Currently, the number of illegal immigrants, residing in the USA, is estimated to be around 15 million people. The largest amount of illegal immigrants reside in the state of California – 2,930,000 people, which is 25% of total population of California. Technically, it means, that each fourth person you see in the street there – is an illegal immigrant! According to the data provided by the Center for Immigration Studies, 56% of illegal immigrants are from Mexico, 22% from other Latin American countries, 13% from Asia, 6% from Europe and Canada, and 3% from Africa.

The European Union suffers from illegal immigration as well. According to data provided by the BBC, 80% of illegal immigrants pass through Grece – many of them through the border with Turkey. Lack of cooperation between Greek police, coast guard and the Turkish army (which is responsible for border control) makes this situation even worse. The majority of the rest of the illegal immigrants to the EU sneak in through the United Kingdom, entering using valid visas, but then overstaying those visas and disappearing into the general population. Currently in the UK, it is estimated. resides between 550,000 and 950,000 illegal immigrants from Africa and Asia.

It is worth mentioning, that because of illegal immigration - legal immigrants are also made to suffer. The Constant flow of illegal immigrants and an inability to properly control it, leaves the host country no other choice, but to take measures to make its immigration policy stricter which in turm makes things harder on legal immigrants as well.

Historical Perspective
From a historical perspective, modern immigration started in the 18th century, accelerated by the slave trade and industrialization. At this time three main types of immigration began to appear: labour migration, refugee migration and urbanization. Because the USA gained independence in the year 1776, while in Europe imperialism was still dominant, at the beginning of 19th century many people immigrated to the USA, which was considered the land of opportunity.

The begining of the 20th century with the fall of the large colonial empires and World War I had it's impact too, as people were immigrating from Europe, driven by the fear of war and violence. The aftermath of World War I was the fall of colonialism and establishment of the League of Nations. At this point, an influx of immigrants from the former-colonies started, which resulted in a large amount of immigrants from the newly independent countries of Africa the former colonies of France, Great Britain, Spain, and the Netherlands.

The League of Nations failed to prevent World War II. The birth of national-socialism in central Europe in 1930s played crucial role in immigration, as many jews started migrating from Europe before the outbreak of World War II. After World War II the United Nations organization was established, which is a sentinel of peace in all the world since then. The roots of the European Union also date back to the late 1940s, when the Paris Treaty was signed.

Since then – the principle of freedom of movement have developped quickly. The newly established Schengen area in Europe allowed the citizens of its member states to move free without any border controls. The United Nations and many countries ratified treaties on freedom of movement and provision of asylum for refugees. However, for the last three decades governments have become very concerned with the problems of terrorism, people trafficing and the drug trade. Therefore, many countries had to reduce the simplicity in their immigration policies in order to improve their homeland security.