Halal chocolate is considered fit for consumption with respect to Islamic dietary guidelines stated in the Quran. Foods that contain unlawful ingredients or are prepared and transported in ways that break these guidelines are considered haram. Halal chocolate doesn't contain unlawful ingredients like alcohol or animal fats and doesn't come into contact with haram substances during processing, transport, or packaging.
Muslims are required to eat only halal food, and practicing Muslims are advised to avoid food or drink if they are doubtful about them. It can be very hard to figure out what chocolate or other foods contain because ingredients can have very fancy names. It's easy to identify food that has gelatin, pork, or alcohol in it if these ingredients are listed directly, but complex terms or substances derived from haram products can easily confuse a person. If a food is considered haram, then boiling, liquefying, or processing it in any way does not change its haram status.
Additives that are derived from haram ingredients are also forbidden. If the ingredients or their sources are not clear, then they fall under the doubtful category, which is called mushbooh. If the chocolate has any mushbooh ingredients, then under Islamic guidelines, it is best to avoid it. Concerned Muslims can call or write to the manufacturer of a company to clarify whether an ingredient is permitted or forbidden.
Chocolate that has ingredients like animal fats or alcohol is haram. If alcohol is used to clean the machinery that makes the chocolate bars, then that chocolate is also considered unfit for consumption for Muslims. If the glue used in the packaging is derived from animal fats, that also makes the chocolate haram. For chocolate to be classified as halal chocolate, not only must it not contain unlawful ingredients, but it cannot be processed or stored or transported in ways or facilities that are haram.
Halal ingredients also cannot come into direct contact with haram food if both are processed in the same facility. Halal chocolate began as a specialty found only in select stores. It has become widely popular and can now be found in popular supermarkets that carry a range of other halal foods. This type of halal chocolate is specifically made by halal companies and marketed as such.
To find out if any popular brand of commonly available chocolate is halal, a careful study of the ingredients is necessary. Some websites carry lists of halal and haram ingredients that may be helpful. Alternatively, some sites list popular chocolates that can be classified as halal chocolate.