"The first year is good preparation for the rest of your life, because parenting is always going to cycle," says developmental psychologist Maureen O'Brien, Ph.D., a mom of twin boys and coauthor of the Watch Me Grow book series. "There will be smooth phases, then your routines will crash and burn periodically."
Thus, the guiding principle of infancy might as well be: Just when you get comfortable, you'll need to change the rules. There are a few constants, of course, and knowing when to expect them can help you across the speed bumps. Here, a guide to the key stages of your baby's first year: