The Sequence-Enforcing (SEQ) gate forces events to occur in a particular order. The input events are constrained to occur in the left-to-right order in which they appear under the gate. That means that the left-most event must occur before the event on its immediate right, which must occur before the event on its immediate right is allowed to occur. The SEQ gate is used to indicate that the output occurs if and only if all input events occurs, when the input events are constraint to occur in a particular order.

The SEQ gate is a dynamic gate, which means the occurrence of the inputs follows a sequential order. In other words, an event connected to a SEQ gate will be initiated immediately after occurrence of its immediate left event. Therefore, if the left-most input is a basic event, then the SEQ gate works like a cold SPARE gate. The SEQ gate can be contrasted with the PAND gate in that the PAND gate detects whether events occur in a particular order (but the events can occur in any order), whereas the SEQ gate allows the events to occur only in the specified order. The first input (left-most input) to a SEQ gate can be a terminal event or outputs of any AND gate, OR gate or dynamic gate, which includes the SPARE gate, PAND gate, FDEP gate or SEQ gate). Only basic events are allowed for all other inputs.