Most children begin recognizing some letters between the ages of 2 and 3 and can identify most letters between 4 and 5. This means that you can start teaching your child the alphabet when he's around 2 — but don't expect full mastery for some time. What's more, toddlers learn differently from older children, so don't pull out the flashcards and audiotapes just yet. Instead, rely on visual aids such as colorful alphabet picture books — your child will have a great time pointing out the letters he knows, as well as colors, shapes, animals, and other objects in the book.
The first step in teaching the alphabet is getting your child interested in listening to stories. At around age 2 or 3, children who are frequently read to get the idea that books contain print, which is made up of letters.
There are lots of fun ways to introduce your child to individual letters. Sign his name to his artwork, then point out each letter one by one. Eventually he'll get the idea that those letters, put together, stand for his name. You can reinforce this identification in many ways: Alphabet letters forming his name on the door of his room, perhaps, or a toy or puzzle personalized with his name. Or help him play with alphabet puzzles or refrigerator magnets that he can manipulate. Once he recognizes a letter, play word games — "What words start with 'B'? Ball, baby, boy ..." or use the first letter of his name as the starting point — "Your special letter is 'P,' for Peter; can you think of any other 'P' words?" (Your child won't be able to write letters until he's about 4, so don't focus on teaching him to write until then.)
If he seems interested, feel free to continue helping your child learn more letters. But if he's under 4 and shows no interest, it's best to let it go for a while. No evidence suggests that very early alphabet learning is related to more advanced reading skills later on.