A circuit breaker module, comprising - a circuit breaker housing having a first housing part and a second housing part; - a switching device; and - at least one first connection module and one second connection module with a connection contact (4, 5) for a connection line; - wherein, in a joined or assembled state, said first and second housing parts (1a, 1b) form a front side and a rear side located opposite said front side and at least one connection side and end faces located opposite one another; - wherein a holding chamber for on of the connection modules is formed on the front side and/or on at least one of the connection sides; - wherein the first and second connection module has a module housing that is formed with a connection opening for a connection line, said connection opening leading to the connection contact (4, 5), and a contact opening; - wherein the connection opening is arranged at that housing side of the module housing that faces toward the front side or the connection side, is flush therewith or forms same when the connection module is inserted into the holding chamber; - wherein the contact opening is arranged at that housing side of the module housing that faces toward a chamber base of the holding chamber when the connection module is inserted into the holding chamber; - wherein the first connection module or the second connection module has a screw terminal as connection contact or is configured as a screw terminal or has a screwless spring terminal as connection contact or is configured as a screwless spring terminal; - wherein the connection contact (4, 5) has a contact element for electrical connection to a coupling contact held by said housing parts (1a, 1b) in the joined or assembled state; and - wherein the coupling contact is accessible via a housing slot, which is formed on the connection side. - a circuit breaker housing having a first housing part and a second housing part; - a switching device; and - at least one first connection module and one second connection module with a connection contact (4, 5) for a connection line; - wherein, in a joined or assembled state, said first and second housing parts (1a, 1b) form a front side and a rear side located opposite said front side and at least one connection side and end faces located opposite one another; - wherein a holding chamber for on of the connection modules is formed on the front side and/or on at least one of the connection sides; - wherein the first and second connection module has a module housing that is formed with a connection opening for a connection line, said connection opening leading to the connection contact (4, 5), and a contact opening; - wherein the connection opening is arranged at that housing side of the module housing that faces toward the front side or the connection side, is flush therewith or forms same when the connection module is inserted into the holding chamber; - wherein the contact opening is arranged at that housing side of the module housing that faces toward a chamber base of the holding chamber when the connection module is inserted into the holding chamber; - wherein the first connection module or the second connection module has a screw terminal as connection contact or is configured as a screw terminal or has a screwless spring terminal as connection contact or is configured as a screwless spring terminal; - wherein the connection contact (4, 5) has a contact element for electrical connection to a coupling contact held by said housing parts (1a, 1b) in the joined or assembled state; and - wherein the coupling contact is accessible via a housing slot, which is formed on the connection side.