Vegetarian and vegan food
This article is a travel topic
Vegetarians and vegans are generally reasonably well catered for in only a few countries. The traditional cuisine and the style of eating in many countries can make it quite difficult for vegetarians or vegans to find food without meat or animal products in it.
Decide before you go whether your reasons for being vegetarian/vegan apply in the country you are visiting. If you feel that consuming products made from animals is wrong, by all means adhere to your regular diet all trip. If you are meat-free because you don't like the treatment of farmed animals in North America then it's probably ok to buy fresh chicken in a market in Thailand.
Take your diet into consideration when planning your trip. Finding vegan cuisine will be easier in Scotland than Nigeria. There will be a greater variety of food available in big urban centers then there will be in rural outbacks. If you want more than anything to visit a tiny village in rural Vietnam, fine, but be prepared to eat a narrow range of dishes or compromise your diet.
Research the cuisine for the place you are going. There will be a couple of vegetable/grain dishes everywhere so you'll have something to order in restaurants. This will also give you an idea of local cooking techniques; often times innocent looking vegetable dishes will be cooked in chicken stock.
Try to find the locations of a few vegetarian/vegan restaurants before you leave. This gives you something to fall back on if you need it. Happy Cow is a great resource which provides the names and locations of many vegetarian and vegan restaurants in cities and towns around the world, including reviews as well.
Most countries in which vegetarianism and veganism are recognised and catered to are western (eg the US, the UK, Australia). The great exception is the Indian Subcontinent where a substantial part of the population are vegetarian. Nearly all restaurants there have a variety of vegetable dishes.
Explaining your diet
In many countries and cultures (especially developing countries where focus is often on getting any sort of food) vegetarian/veganism is very rare or unheard of. People will feel insulted when you turn down the lamb kabobs they have prepared for you. Come up with a short explanation and be prepared to repeat it. If you're vegetarian/vegan for non-religious ethical reasons, in places with a language barrier or strong food/host tradition it's usually best to refrain from explaining out your beliefs and go with something inarguable (medical reasons, something vaguely religious or cultural). Be polite and apologetic as you would anywhere.
In some cultures, there may be an internal vegetarian tradition of some kind that you can compare your diet to. In countries with Buddhist sub-populations, some vegetarian travellers find that calling their diet "Buddhist" is the simplest way to explain it.
Be as considerate as you are in your home country. If you are staying long term with someone or eating dinner at their house, let them know about your diet. Ask if you can bring food, give them examples of common local vegetarian dishes. Let them know that you don't mind them eating meat/milk/eggs/cheese.
When all else fails, hit the grocery store/local veggie market. You can cobble something together with a camping stove or get an apartment with a kitchen.