Technologies are described herein for customized identifier (“ID”) generation by an ID service. One or more calling components (“components”) remote from the ID service generate requests for IDs. The requests can include one or more rules defining how the IDs are to be generated, type data identifying a type of IDs to be generated, encryption data specifying whether, and if so, how the IDs are to be encrypted, and number data defining how many IDs are to be generated at a particular time. The ID service receives the request, and in response to the request, generates the number of IDs specified, in accordance with the rules, type data, and encryption data provided in the request. An ID database can store one or more of the IDs and/or rules associated with the components, such that each component can be relieved from maintaining its own database for ID operations.