Veggie

If you are going for ovo-lacto vegetarian:

No meat (of course). This includes birds like chicken and also fish. - I know it is a bit weird to point this out, but I have heard of people who thought they where vegetarians and ate chicken.

Might wanna cut out gelatin, because it is made from bones. That means finding gummy bears etc. is harder, but not impossible (have a look at your local wholefoods store. There are also pure vegetarian shops around).

Find out which cheese has vegetarian rennet. If you live in the US this should be pretty easy, or so I have heard. If you live in Europe it's a bit harder to find. Non vegetarian rennet is made from something out of calves stomachs.

Might have to decide how you feel about shellac (used to coat certain food to make it nice, sleek and shiny) and certain food dyes, which are won from stuff that comes from bugs.

Decide how you feel about uncertainties of all of the above when going to restaurants.

Fishsauce is used in a lot of Thai cooking. Might wanna ask to hold that, it should not be to much of an hassle for them, but food will taste a bit less "Thai" .

Mc Donald's fries in the us are not vegetarian. They are fine in several other countries, though.

There are Anchovies in cesar salad dressing. So, fish... might wanna avoid that.

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If you are going for Ovo-Vegetarian:

The above, just on top: No cheese at all, no milk products of any description. More food checking because milk products sneak into a lot of things.

Check out some alternative "milks", like Almond milk and soy milk. Try your way through different ones and different brands. Soy milk from one brand does not taste like the soy milk from another one.

If you read "lactic acid"on something, don't worry, though. Misleading name, but it is fine.

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If you are going for Lacto-Vegetarian:

The list I created at the beginning, plus nothing with egg in it. Again, check food lables for sneaky egg. It's a litle bit less often sneaking in than milk products, though.

Might wanna look up some vegan baking receipes, so that you can have some baked treats from time to time.

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If you are going for Vegan:

Above list, plus restrictions for Ovo-Vegetarians and Lacto-Vegetarians.

Think if you want to use honey. Officially vegans don't, but some people who call themselves vegan do, if it comes from very selected sources.

Non-food issue: Wool and leather. Vegans generally don't use either, even though new vegans often use old ones up and some vegans might not mind buying the items if they are second hand and in a charity shop.

Basically nothing that comes from animals.

Please make sure you get a B-12 supplement. It is important, but the one thing humans really can not get on a vegan diet without supplemention. Some other things are harder to get, but still possible at least.B-12 defficency is nothing to joke about.

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Now, general tips: Read up on stuff. Read up on nutrition, on the concepts behind vegetarianism/veganism, on perceived and actual dangers and how to avoid them. The more you know the better you can argue your decicions.

Get yourself some cook books and learn to cook. There are vegetarian cook books that cater to poor college students.

Lentils and any kind of beans are your friends. They have a nice amount of protein, are cheap and can be used so many ways. Find out where to buy them in bulk, cook bigger amounts and store them in tupperware in your fridge or freeze them.

Cooking for yourself or for friends: Bean chillis are good for either, as if you coook only for yourself you can store the reaminins and eat over a few days. Or you can make a big pot and serve all your friends. Another good thing for everybody is stir fry. There is much more, but those are, to me, the two best things.

Going out to eat: Check the menu in advance if you know where you are going. If there is nothing vegetarian look for something that might be modified. If you want to phone the place in advance and ask if that would be fine. Burrito places generally have black bean burritos, so should be fine. Some burger places have vegetarian burgers. Pizza Margarita is really nice as are most other vegetarian pizzas, if you don't want cheese on your pizza you can always ask for it to be hold (and yeah, cheeseless pizza still taste's good). Most kebab places also have fallafel. Asian restaurants have a lot of vegetarian stuff but you might want to ask about fishsauce or oyster sauce. Vegetarian sushi is GREAT!

Don't freak out: You will slip. You might go somewhere and eat the fries as the only vegetarian thing you see but later learn they had beef seasoneing. No big deal, you know from now on. You might think it's a waste your friend's last peace of pepperoni pizza end's in the rubbish and you eat it and then you feel guilty. It's ok, you no know that doing this does not make you happy so you can avoid it next time. You might just not know if the pizza cheese hasvegetarian rennet. Don't worry to much aobut this detail, just do as much as you are comfortable with.

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Hope I could help (and did not overload you). If you have questions feel free to PM me.

A great resource is veggieboards.com

I'm also a fan of anything by Dr. Neal Barnard and the PCRM (Physicians Committee for Responsible Medicine)

I am a 3-year vegetarian who is dabbling in veganism

AndreannaTami has had some really great and helpful tips! However, she is thinking more along the lines of a vegan lifestyle though. A vegan diet is one that does not include anything containing something from an animal. A vegetarian diet is mainly a diet without animal flesh (some will remove eggs as well).

If you do want to become vegan AndreannaTami has had some great tips as most of the tips she listed are for a vegan lifestyle. Don't forget marshmallows, jello, beauty products and even sugar is not vegan.

Ensure it's something you want to do as it can be a little rough at the beginning to get proper nutrition in. Do your research. Figure out what "rules" you will go by. I am a vegetarian however I do consume dairy and eggs. I have drastically cut back and one day soon I will cut out all animal products as it's something I am passionate about... however at the moment I do consume them as they are cheaper options in terms of some nutrients.

For when you eat out, don't be shy to ask for substitutions. A lot of places will put extra veggies in your meal instead of the meat.

I personally don't try to always substitute meat products. They are processed and filled with sodium normally. I do still keep veggie burgers in the freezer so when I go to a BBQ for example at a friends house I can throw one on the grill and not feel totally left out.