So much happens in the first year of life that it's necessary to measure age in weeks and months. After the one year mark, you may stop counting those small spans of time...until you look up one day and you realize that this child is not a "one-year-old." She communicates too clearly (even if her specific words are still a jumble of sounds)and handles her self more steadily (even if she continues to stumble and bump her way around a bit) and, perhaps most noticeable, her fierce desire for independence has multiplied tenfold.
Toddlers hit milestones at different ages, of course, but by the year-and-a-half mark, you will likely see some very common skills emerge in the areas of:
See Also: Toddler Development Age 1 | Toddler Development Age 2 | Toddler Development Age 3