In Tellico, a collection is the document. Only one collection exists in each Tellico file. A collection contains any number of fields and entries. Tellico supports 12 specific collection types by default: books, bibliographic entries, comic books, videos, music, trading cards, coins, stamps, video games, wines, board games, and file listings. In addition, an empty generic collection template is available for any other type of collectibles or lists.

Each collection may have an unlimited number of fields. Tellico supports eleven types of fields, which allow for a range of different data. The fields can be edited with the Collection Fields Dialog and are explained further in the Field Types section.

An entry is the basic record in Tellico. Each entry contains a single value for each field in the collection. A collection may have an unlimited number of entries, in theory, although since the whole collection is always resident in memory, too many entries could slow down the application.

Tellico has been tested with a collection of 10,000 entries, and the speed was satisfactory. However, if many large images are included in the collection, the loading and processing time does slow down greatly. Performance can be improved by having Tellico store images separate from the data file itself, either in the application-specific folder or a folder relative to the data file. More information can be found in the configuration section.