Checking visa requirements for the countries you're visiting is essential. There's nothing worse than arriving somewhere and being told you can't enter because you haven't got the right paperwork.

So, what is a visa? In short, it's a stamp or form placed in your passport when you enter (and sometimes when you leave) a foreign country. It shows permission to travel to, enter, transit or stay in a country. It doesn't guarantee entry - that remains the right of the country's immigration officers.

What do you do to get the required visas? If you're organising your itinerary independently of a travel agency, you need to check with the embassies of each of the countries you're planning to visit. If you're organising your itinerary through an agency, they should be able to advise you.

The rules for entry vary, so it's worth checking ahead of time. Here are some of the things you may need to bear in mind.

Application times Application times vary. It could take weeks, or you could pick up your visa online or on entry to the country.

Cost Visas are sometimes free, but they can also cost up to 50 or 60.

Length of time on your passport To enter some countries your passport must still be valid for up to eight months.

Airline tickets To get some visas you have to be able to show your airline tickets on application. In other cases, you must be able to prove you have an onward ticket from the country.

Jabs Some African countries insist you have a Yellow Fever certificate.

Medical insurance It's worth checking the requirements for medical insurance. However, if you're travelling around the world, it's highly recommended that you get insurance anyway.

Maximum stay All countries quote a maximum amount of time you can stay. Make sure this fits with your schedule.

Invitation In rare cases, to visit a country you will need a letter of invitation.

Funds In other rare cases, you will need to prove that you have sufficient funds to stay in the country - and also enough money to leave.

Clothing Check clothing requirements, as some countries refuse entry to people who don't comply with rules for general appearance.