Colic (also known as infant colic, three month colic, and Infantile colic) is a condition in which an otherwise healthy baby cries or screams frequently and, for extended periods, without any discernible reason. The condition typically appears within the first two weeks of life and almost invariably disappears, often very suddenly, before the baby is three to four months old, but can last up to 12 months of life. One study concludes that the chances of having colic is lower in breastfed babies.

The crying often increases during a specific period of the day, particularly the early evening.

The medical definition of colic is a condition of a healthy baby in which it shows periods of intense, unexplained fussing/crying lasting more than 3 hours a day, more than 3 days a week for more than 3 weeks. However, many doctors consider that definition, first described by Morris Wessel, to be overly narrow and would consider babies with sudden, severe, unexplained crying lasting less than 3 hours/day as having "colic" (so-called "non-Wessel's" colic).

Persistent infant crying is much more than a parenting nuisance. Crying and the exhaustion associated with it can trigger serious problems, such as relationship stress, breastfeeding failure, shaken baby syndrome (also known as abusive head trauma - the leading cause of child abuse fatalities), postpartum depression (affecting 10-15% of new mothers and many new dads), excess visits to the doctor/emergency room (1 in 6 children are brought to the doctor/emergency rooms for evaluation of persistent crying),unnecessary treatment for acid reflux and maternal smoking. Crying and exhaustion may also contribute to SIDS and suffocation (from agitated babies flipping onto their stomachs, concerned parents placing fussy babies on the stomach to sleep, tired parents falling asleep with their baby in unsafe places - like couches or beds with bulky covers), infant obesity,maternal obesity and even automobile accidents.