Breeding and Eggs

Breeding is very important in the Pokémon games. Breeding was introduced in Gold and Silver, and it has been in every game since then. It allows you to get more than one of your starter Pokémon, get the rare Pokémon, Phione by breeding a Manaphy, as well as getting extra Pokémon such as Tyrogue. You can put two Pokémon in the Day Care Center in every game starting with Gold and Silver, and after every 255 steps that you take, your Pokémon have a chance of making an egg.

Pokémon can breed only if they are in the same Egg Group and one is male and one is female. An example of Pokémon that could breed would be a female Gloom and a male Weepinbell, as they are both in the Plant egg group. The female Pokémon will be the one that the baby will turn out to be, in its lowest form, so in this example, an Oddish would hatch from the egg. Ditto is also an important Pokémon in breeding because it can breed with any Pokémon that can breed, even male Pokémon, but the egg that is bred will never be a Ditto, but instead the lowest form of the other Pokémon in the Day Care.

Male Pokémon are useful too, because they can pass on moves to the baby such as Earthquake, a hard to obtain TM in some games. Moves that can be passed on from the male father are called Egg Moves, and are often TMs or moves that can be learned by level up by the female Pokémon that is also in the Day Care.

Once you get the Egg, depending on what Pokémon is in it, it will hatch after so many steps. Most Pokémon hatch after taking 5,120 steps, but some hatch with more steps and some with less. Every step you take ingame when a Pokémon is in the Day Care will also give it that much Experience. For example, if you walked 500 steps after putting a Pokémon in the Day Care, the Pokémon would gain 500 experience. Pokémon that learn a move upon level up while in the Day Care will automatically learn it and replace the first move in its move slots.

Also, starting in Emerald, if you have a Pokémon that has the Ability Magma Armor or Flame Body in your party, eggs will hatch in half the amount of steps normally needed. In some games, it is also possible to breed Pokémon eggs with increased chances of the egg being shiny upon hatching. For more information about shiny breeding, check the Shiny Pokémon page.

Red, Blue, and Yellow

You can't actually breed in Pokémon Red, Blue, and Yellow, but there is a Day Care. Just south of Cerulean City, a man will raise your Pokémon depending on how many steps you keep them in there. In these games, you can only store one Pokémon in the Day Care.

Ruby, Sapphire, and Emerald

The Day Care Center is on Route 117 in these games, right in between Mauville City and Verdanturf Town. The Day Care Lady will take two of your Pokémon and after walking or biking 256 steps, if they're in the same egg group, they have a chance of breeding. The Day Care Man will step out a little from his usual position to indicate that your Pokémon have laid an egg. Starting in Emerald, by having a Pokémon with Flame Body or Magma Armor as an ability in your party (a list of Pokémon is below), the steps needed to hatch an egg in your party is cut in half. This really helps speed up egg hatching.
If you talk to the old lady right below the Hot Springs in Lavaridge Town, she'll offer to give you a Wynaut egg. After walking with it for 5,120 steps, it will hatch and you can enjoy it!

Diamond, Pearl, and Platinum

The Day Care is in Solaceon Town in these games. When you go inside for the first time, put a Pokémon in the Day Care and get the Pokétch App #9 for checking on your Pokémon on the go. After you put compatible Pokémon in the Day Care, watch the Pokétch App for your Pokémon in there and walk or bike 255 steps. You'll have to press the Pokétch screen to refresh the status of your Pokémon on it, but going inside or outside of buildings will refresh it too. As well as checking the Pokétch, you can see if the Day Care Man turned toward the right to know if an egg has been bred.
Also in Diamond, Pearl, and Platinum, you get a Happiny Egg from a Hiker in the southeast corner of Hearthome City, which takes 10,240 steps to hatch.

HeartGold and SoulSilver

The Day Care is in a different place in Johto; it's right before you get to Goldenrod City, on Route 34. When you get here, you can put two different Pokémon in there by talking to the Day Care Lady, the wife of the Day Care Man. After you walk for 255 steps, you'll have a chance at getting an egg. One thing different in these games is that if you talk to the Day Care Man, he'll let you get his PokéGear number. You can check on your Pokémon by calling him when you're far away from the Day Care. You can also have him call you when your Pokémon have breed an egg.
You also get a Togepi Egg from Professor Elm's assistant after Professor Elm calls you when you beat Falkner. You can pick up this egg in the Violet City Poké Mart. Togepi hatches after only 2,560 steps.

Black, White, Black 2, and White 2

On Route 3, just after Striaton City, the Day Care Lady can take two of your Pokémon and if they are in the same egg group, they will breed, just like in previous games. One difference in these games though, is that if you have an open slot in your party and your Pokémon make an egg, the Day Care Man will call you over, telling you that your Pokémon have made an egg. This makes up for the lack of PokéGear or him facing a different way than normal, since he always faces down in Black, White, Black 2, and White 2.
In the rest house of Route 18 in Black and White, a Ranger will give you a Larvesta egg, which hatches after 10,240 steps. In Black 2 and White 2, a Breeder in Nacrene's west gate will give you a Happiny egg, which also hatches after 10,240 steps.

X and Y

In X and Y, the Day Care Center is on Route 7. The general premise is the same, though one difference in these games is that the Day Care Man will turn around until he has an egg. Another difference is that female Pokémon can pass down egg moves, and breeding a female parent Pokémon in a different Poké Ball (for example, one that was caught in a Great Ball) will cause the eggs to be laid by it to also be in that Poké Ball, instead of the standard Poké Ball, like in previous games. So, for example, a female Poliwhirl caught in a Dive Ball and a male Poliwhirl caught in a Poké Ball will breed Poliwag eggs that are "caught" in Dive Balls.

That’s about all there is to breeding! Hope this helps to hatch good Pokémon.

Pokémon with the Flame Body or Magma Armor Abilities
(Other abilities also listed, with hidden abilities in brackets)

Happy breeding!