The Boa constrictor is an almost unique instance of an animal having the same common and scientific binomial name. There are 10 subspecies, all of which are referred to as "Boa constrictors".

The females are generally significantly larger, in both length and girth, than the males. The average size of a mature female boa is between 7-10 ft, whilst it is only 6-8 ft for the males. It is common for female individuals to exceed 10ft, particularly in captivity, where lengths of up to 12ft or even 14ft can be seen. Other examples of sexual dimorphism in the species include the fact that males generally have longer tails to contain the hemipenes and also longer cloacal spurs, hind leg remnants, which are used to grip and stimulate the female during copulation

Boa constrictors have an arrow-shaped head that has very distinctive stripes on it. One runs dorsally from the snout to the back of the head. The others run from the snout to the eyes and then from the eyes to the jaw.

As semi-arboreal snakes, young boa constrictor individuals may climb into trees and shrubs to forage, however they become mostly terrestrial as they become older and heavier.

Boa constrictors are ambush predators and as such will often lie in wait for an appropriate prey to come along at which point they will attack. However, they have also been known to actively hunt, particularly in regions with a low concentration of suitable prey, and this behaviour generally occurs at night. The boa will first strike at the prey, grabbing it with its teeth, it then proceeds to constrict the prey until death before consuming it whole. Their teeth also help force the animal down the throat whilst muscles then move it towards the stomach. It will take the snake approximately 4-6 days to fully digest the food, depending on the size of the prey and the local temperature. After this the snake may not eat for anywhere from a week to several months, due to its slow metabolism.