Gelatin desserts are desserts made with sweetened gelatin.

They can be made by combining plain gelatin with other ingredients, or by using a premixed blend of gelatin with other additives. Popular brands of commercial mixes include Jell-O and Knox gelatin from Kraft Foods in North America, Royal in Argentina and Uruguay, Hartley's (formerly Rowntree's) in the United Kingdom and Aeroplane Jelly in Australia.

Fully-prepared gelatin desserts are marketed in a variety of forms, ranging from large decorative shapes to individual serving cups.

To make a gelatin dessert, gelatin is dissolved in hot liquid with the desired flavors and other additives. These latter ingredients usually include sugar, fruit juice, or sugar substitutes; they may be added and varied during preparation, or pre-mixed with the gelatin in a commercial product which merely requires the addition of hot water.

In addition to sweeteners, the prepared commercial blends generally contain flavoring agents and other additives, such as adipic acid, fumaric acid, sodium citrate, and artificial flavorings and food colors. Because the collagen is processed extensively, the final product is not categorized as a meat or animal product by the US federal government.

Prepared commercial blends may be sold as a powder or as a concentrated gelatinous block, divided into small squares. Either type is mixed with sufficient hot water to completely dissolve it, and then mixed with enough cold water to make the volume of liquid specified on the packet.

The solubility of powdered gelatin can be enhanced by sprinkling it into the liquid several minutes before heating, "blooming" the individual granules. The fully dissolved mixture is then refrigerated, slowly forming a colloidal gel as it cools.

Gelatin desserts may be enhanced in many ways, such as using decorative molds, creating multicolored layers by adding a new layer of slightly cooled liquid over the previously-solidified one, or suspending non-soluble edible elements such as marshmallows or fruit. Some types of fresh fruit and their unprocessed juices are incompatible with gelatin desserts; see the Chemistry section below.

When fully chilled, the most common ratios of gelatin to liquid (as instructed on commercial packaging) usually result in a custard-like texture which can retain detailed shapes when cold but melts back to a viscous liquid when warm. Higher gelatin ratios can be used to increase the stability of the gel, culminating in gummy candies which remain rubbery solids at room temperature.