If you find an egg in your travels, you're in luck: A Pokemon is baking inside, which could potentially turn into a powerful new addition for your team. Eggs first appeared in the Generation II games and still appear in the series to this day. The hatching of an egg coincides to the steps taken in-game rather than the current time and date; the more you walk, the quicker the egg will hatch.
Minimum Steps to Hatch
When you have an egg, you need to walk a certain number of steps to hatch it. Most Pokemon need at least 5,355 steps, but there's no specific number required; some can hatch much earlier, like Magikarp at 1,530 steps, and some take much longer, like Lapras at 10,455 steps. In Pokemon gaming terms, the term "egg cycle" refers to 255 steps, so your average Pokemon takes about 21 egg cycles to hatch. When you get an egg, try hopping on the bike; you move twice as fast, so the egg will hatch twice as quickly than if you warmed it up on foot. You can also surf or use the Roller Skates in "Pokemon X/Y."
Checking on an Egg
When you interact with an egg in your inventory, you'll see a quote estimating how many cycles remain before it'll hatch. For the first quarter of the egg's life, you'll see "this Egg will take a long time yet to hatch." The quotes change as each quarter passes, until you see the message "This Egg will hatch soon." When an egg is ready to hatch, you'll receive a pop-up message that interrupts your travels before revealing the Pokemon inside.
Getting a New Pokemon Egg
It's possible to get eggs in-game without breeding, such as by getting Togepi before leaving Violet City in "Pokemon Omega Ruby" and "Pokemon Alpha Sapphire." For the most part, though, you'll have to breed the eggs yourself. On Route 117 of the aforementioned games, you'll find the Pokemon Day Care. Leaving two Pokemon from the same egg group at the daycare facility, such as Monster group members Bulbasaur and Squirtle, gives you a good chance at creating an egg containing a baby Pokemon.
Tips for Breeding and Hatching Pokemon
To breed Pokemon, the two dropped off at the Day Care must be a male and female of the same egg group: Monster, Field, Fairy, Dragon, Flying, Bug, Mineral, Human-Like and many others. Genderless Pokemon, on the other hand, cannot reproduce. The only exception is Ditto, who can reproduce with any Pokemon to make a copy of that Pokemon. Eggs take up space in your party lineup as well, and they can't fight; remember to change your Pokemon before challenging the gym leader, or the yoke will be on you.