The Sri Lanka Postal Service has issued a wide variety of stamp categories over the years, reflecting different themes and subjects. Here are some of the main stamp categories that have been issued in Sri Lanka:

1. Commemorative stamps: These stamps are issued to mark important events, anniversaries, and milestones, such as Independence Day, religious festivals, or the opening of a new building or institution.
2. Definitive stamps: These stamps are the regular, everyday stamps used for postage. They feature standard designs and are often issued in multiple denominations to accommodate different postal rates.
3. Thematic stamps: These stamps are issued around a particular theme, such as wildlife, sports, or cultural heritage. They may feature images of people, places, or objects related to the theme.
4. Joint issue stamps: These stamps are issued in partnership with other countries, featuring shared themes or designs. They are often used to promote international friendship and cooperation.
5. Souvenir sheets: These are sheets of stamps that are often issued in conjunction with commemorative stamps, featuring larger images or designs. They are typically used for collecting and display purposes.
6. First Day Covers: These are special envelopes that are postmarked on the first day that a stamp is issued, and often feature a commemorative design or image. They are often collected by stamp enthusiasts.
7. Maximum cards: These are postcards that feature a stamp and a matching image or design, with the stamp affixed to the front of the card. They are often used to showcase a particular stamp or theme