A chocolate bar is a confection containing chocolate, which may also contain layerings or mixtures that include nuts, fruit, caramel, nougat, and wafers. A flat and easily partitionable chocolate bar is also called a tablet. In some varieties of English and food labeling standards, the term chocolate bar is reserved for bars of solid chocolate, with candy bar used for products with additional ingredients.

The manufacture of a chocolate bar from raw cocoa ingredients requires many steps, from grinding and refining, to conching and tempering. All these processes have been independently developed by chocolate manufacturers from different countries. There is therefore no precise moment when the first chocolate bar came into existence. Solid chocolate was already consumed in the 18th century. The 19th century saw the emergence of the modern chocolate industry; most manufacturing techniques used today were invented during this period.

Dark, milk and white are the main three types of chocolate. Ingredients not derived from cocoa have been added to bars since the beginning of the chocolate industry, often to reduce production costs. A wide variety of chocolate bar brands are sold today.

In many varieties of English, chocolate bar refers to any confectionery bar that contains chocolate. In some dialects of American English, only bars of solid chocolate are described as chocolate bars, with the phrase candy bar used as a broader term encompassing bars of solid chocolate, bars combining chocolate with other ingredients, and bars containing no chocolate at all. In Canada, while the term chocolate bar is commonly used for bars combining chocolate with other ingredients, only bars of solid chocolate can be labelled as a chocolate bar.

The term bar may refer to a large variety of shapes, including not oblong ones, such as squares. Small (bite-sized) chocolate pieces are however usually referred to as chocolates, regardless of shape. These include neapolitans, bonbons, pralines and truffles.

Cake chocolate is an old commercial designation for solid chocolate.

Solid chocolate was probably already consumed in pre-Columbian America, in particular by the Aztecs, despite the beverage being the traditional form of consumption of cocoa in Mesoamerica. In fact, any finely ground cocoa that is not immediately used to make a drink turns into solid chocolate. The grinding of the cocoa beans was done with a stone metate. Dominican friar Diego Durán mentions in his writings that Aztec soldiers carried small balls of ground cocoa among other military rations. Cocoa was introduced into Europe in the early 16th century, possibly already under its processed (solid) form.

Until the 18th century, chocolate was essentially consumed as a drink. Transport of cocoa beans was slow and difficult, therefore making the product very expensive in Europe. Chocolate was usually sold as a solidified ground but still grainy cocoa paste (in the form of blocks, sticks or balls) to be dissolved in water or milk, either plain or already sweetened and flavoured. It is unclear when bars or tablets of chocolate (meant to be eaten straight as a candy rather than grated into a drink) were made for the first time. It is known, however, that the consumption of solid chocolate by the wealthy increased by the end of the 18th century.