Paris is one of Europe's culinary centres. The restaurant trade began here just over 220 years ago and continues to thrive. It may however come as a surprise that Paris isn't considered the culinary capital of France, rather some people prefer the French cooking found in small rural restaurants, outside of the city, closer to the farms and with their focus on freshness and regional specialities. Even amongst French cities, Paris has long been considered by some people as second to Lyon for fine dining.
There have been other challenges in the last 20 years or so as restaurateurs in places like San Francisco and Sydney briefly surpassed their Parisian fore bearers, again with an emphasis on freshness of ingredients but also borrowings from other cuisines. Parisian cooks didn't just rest on their laurels during this time, rather they travelled, taught, and studied, and together with Paris's own immigrant communities, have revitalized the restaurant trade. Today you can find hundreds of beautiful restaurants with thoughtful (or just trendy) interior design and well-planned and executed cartes and menus offering a creative mélange of French and exotic foreign cuisines. It's safe to say that Paris is once again catching up with or edging ahead of its Anglophone rivals.
Of course there are also some traditional offerings, and for the budget conscious there are hundreds of traditional bistros, with their sidewalk terraces offering a choice of fairly simple (usually meat centred) meals for reasonable prices.
For the uninitiated, it is unfortunately possible to have a uniformly poor dining experience during a stay in Paris, mainly because many attractions are situated in upscale areas of town, and that mass tourism attracts price gougers. It is frequent to hear of people complaining of very high Parisian prices for poor food and poor service, because they always tried to eat close to major tourist magnets. Try to go eat where the locals eat for good food and great service.
Many restaurants are tiny and have tables close together - square metres are at a premium and understandably restaurateurs need to make the most of limited space. In some cases when the restaurant is crowded, you may have to sit beside strangers at the same table. If that does not appeal to you, go to a more upscale place where you will pay for the extra space.
Trendy restaurants often require reservations weeks, if not months in advance. If you haven't planned far enough ahead, try to get a reservation for lunch which is generally easier and less expensive.
For an easy-to-manage eating budget while in Paris, consider: breakfast or "petit dejeuner" at a restaurant, possibly in your hotel, consisting of some croissants, coffee, and maybe a piece of fruit. Get a 'walking lunch' from one of Paris' many food stands--a panino in the centre of the city, a crepe from a crepe stand, a felafel pita or take-out Chinese in the Marais. Traiteurs serving Chinese food are ubiquitous in the city and good for a cheap lunch and many patisseries sell inexpensive coffee and sandwiches. All these are cheap (about the same as breakfast), easy, and allow you to maximize your sightseeing and walking time while enjoying delicious local or ethnic food. For dinner, stroll the streets at dusk and consider a €20-40 prix-fixe menu. This will get you 3 or 4 courses, possibly with wine, and an unhurried, candlelit, magical European evening. If you alternate days like this with low-budget, self-guided eating (picnicking, snacking, street food) you will be satisfied without breaking the bank.
If one of the aims of your trip to Paris is to indulge in its fine dining, though, the most cost-effective way to do this is to make the main meal of your day lunch. Virtually all restaurants offer a good prix-fixe deal. By complementing this with a bakery breakfast and a light self-catered dinner, you will be able to experience the best of Parisian food and still stick to a budget.