All babies need to learn to 'sleep'. Either the caretakers teach them or they find a sleep pattern on their own. We didn't CIO (cry it out), we simply enacted a sleep time and routine (as well as a flexible nursing/food schedule), that we enforced on ourselves (parents) without many variations. Babies need clues to be reinforced to feel 'safe' and fall asleep. Our child will NOT sleep for more than 8 hours, so we settled on a bed time of 10pm to 6am, nursing/bottles every 3 hours from 6am to 9pm. After the baby feeding at 6am, morning routine, diaper change and a bit of play in the crib, she sleeps from 7am to 8:30am, without prompting or supervision.
This routine began at 3 months and continues into her 7th month. She regularly naps during the day, which is very important, if she is to fall asleep promptly at 10pm. Check out the literature on baby sleep/child development at the Library, it was very informative and helpful to us.