Microwave popcorn is a convenience food consisting of unpopped popcorn in an enhanced, sealed paper bag intended to be heated in a microwave oven. In addition to the dried corn, the bags typically contain cooking oil with sufficient saturated fat to solidify at room temperature, one or more seasonings (often salt), and natural or artificial flavorings or both.

The bag is typically partially folded when it is placed in a microwave, and inflates as a result of steam pressure from the heated kernels.

Microwave popcorn bags are designed to avoid popped-kernel scorching, an undesirable effect that takes place when popped kernels are heated above 300 °F (150 °C). A susceptor—usually a metalized film laminated onto the paper of the bag—absorbs microwaves and concentrates heat at the film interface, thus ensuring a heat distribution focused on the hard-to-heat flavor coating so that the unpopped kernels are evenly coated prior to popping, thereby ensuring even flavor throughout the product.

Some popcorn is flawed and will not pop because of possible damage to the shell, which allows the steam to escape. These unpopped kernels are known as "old men" or "grandpas".

An early susceptor popcorn bag design was patented by The American Company General Mills in 1981 (US Patent #4,267,420).

The first use of microwaves to pop corn kernels was when Raytheon engineer Percy Spencer further tested his observation of a nut candy bar melting in his pocket while working with radar tubes during WWII.^{[citation needed]}

Care in package design is needed for food safety.

A safety issue is that the cooking time given on the packaging does not apply to all microwave ovens. Setting the timer and coming back later, after the timer's alarm has sounded, could result in the popcorn being burnt and smoking badly. Microwave popcorn makers suggest that the person cooking the popcorn stay near the oven to observe the popcorn as it cooks, and take the popcorn out when the time between pops is more than a few seconds.