An electronic device includes a host module and a first expansion module. The first expansion module has a first wall and a second wall substantially parallel to the first wall. A host connector is located on the second wall. The first expansion module includes a first coupling wall and a first expansion wall substantially parallel to the first coupling wall. A first coupler is located on the first coupling wall. The first expansion module can be stacked on the host module where the first coupling wall contacts the second wall. The first coupler is electrically and detachably coupled to the host connector.