Hatching Eggs

Eggs (not Lucky Eggs) are acquired from spinning PokéStops or Gyms, and are hatched to produce Pokemon. Eggs are listed separate from Items and Pokemon (but they DO count against your Pokemon storage total and appear in the right tab of the Pokémon storage).

Eggs come in 2Km, 5Km, or 10Km varieties, and the pool of available Pokemon for each type tends to change over time. In general, more common Pokemon tend to be found in 2Km and 5Km eggs, while 10Km eggs tend to have rarer (and often non-nesting) Pokemon (Niantic has had events where 2Km eggs spawned special Pokemon to prompt more walking and incubating during certain events). Even within egg distance-types, there tend to be distributions of the possible Pokemon, where some Pokemon are rarer hatches than others. 

Everyone starts the game with one Egg Incubator ∞, which is colored orange. It may be used to hatch as many eggs as desired. Each incubator can only hold one egg at a time, though, which cannot be unslotted.

Normal Egg Incubators may also be acquired from rewards for leveling up or from the PokéCoins shop. Super Incubators may also be bought from the PokeCoins shop (although these have been limited to during special events). The "regular" and Super Incubators can only be used 3 times before disappearing, so save them for longer-distance eggs. Super Incubators hatch eggs 33% faster than regular/permanent incubators.

Egg-hatching distance must be walked while the game is active or minimized/lock screened when using GO+, or the distance will not count. This is based on GPS-measured distance and not on number of steps like a pedometer.

• Pokémon hatched from eggs appear to have CP based on the trainer level when the Egg is first acquired, so saving them for higher level won't help.
• Similarly, the Pokemon inside the egg seems determined when the egg is acquired, so if an event is announced where certain eggs will have special Pokemon, some people hatch many/all their "old" eggs before the event, so they only collect "new" eggs after the event starts (stop spinning PokeStops/Gyms---to avoid the possibility of getting another egg---or else fill up the Pokemon storage before starting to hatch eggs---this allows a trainer to keep spinning PokeStops and Gyms, since no new eggs can be acquired if there is no more Pokemon storage space).
• Once the trainer reached level 20, any egg picked up will always hatch at level 20.  This means hatched Pokémon usually have higher CP than most wild Pokémon encounters of the same type.
• Pokémon hatched from eggs tend to have much higher IV scores than wild catches because individual IVs will be in the 10-15 range (well above what is expected of the usual uniform distribution between 0-15 for wild-caught, non-weather-boosted Pokemon). Hatches will appraise in the second-highest or highest groups.
• The maximum speed that an individual can travel to hatch Pokemon is roughly ~6.5MPH (10.5km/h).  Traveling faster, such as by car or bike, and Pokemon GO may discard your distance traveled.
• Boost XP or stardust hauls from hatching eggs by placing several of same-distance eggs in incubators at the same time. Monitor the distance, and use a Star Piece, Lucky Egg, or both just before hatch.