An electrowetting on dielectric (EWOD) device comprising: a first substrate assembly and a second substrate assembly respectively defining an inner surface and an opposing outer surface, wherein the first and second substrate assemblies have opposing inner surfaces; wherein the opposing inner surfaces of the first substrate assembly and the second substrate assembly are spaced apart to define a channel between the opposing inner surfaces of the first and second substrate assemblies, and wherein one of the first or second substrate assemblies includes electrowetting electrodes for controlling movement of a droplet of fluid in the channel of the EWOD device; a housing for receiving at least one of the first substrate assembly and the second substrate assembly , the housing comprising an alignment feature for locating at least one of the first and second substrate assemblies within the housing; and a fixing feature for fixing the at least one of the first and second substrate assemblies within the housing; wherein the second substrate assembly is located within the housing such that the outer surface of the second substrate assembly is an outer component of the EWOD device; and wherein the EWOD device includes one or more fluid input structures for loading and/or extraction of fluid into/from the channel of the EWOD device; wherein the housing extends around the lateral side edges of the first and second substrate assemblies , around only a peripheral portion of the outer surface of the first substrate assembly , and around only a peripheral portion of the inner surface of the second substrate assembly . a first substrate assembly and a second substrate assembly respectively defining an inner surface and an opposing outer surface, wherein the first and second substrate assemblies have opposing inner surfaces; wherein the opposing inner surfaces of the first substrate assembly and the second substrate assembly are spaced apart to define a channel between the opposing inner surfaces of the first and second substrate assemblies, and wherein one of the first or second substrate assemblies includes electrowetting electrodes for controlling movement of a droplet of fluid in the channel of the EWOD device; a housing for receiving at least one of the first substrate assembly and the second substrate assembly , the housing comprising an alignment feature for locating at least one of the first and second substrate assemblies within the housing; and a fixing feature for fixing the at least one of the first and second substrate assemblies within the housing; wherein the second substrate assembly is located within the housing such that the outer surface of the second substrate assembly is an outer component of the EWOD device; and wherein the EWOD device includes one or more fluid input structures for loading and/or extraction of fluid into/from the channel of the EWOD device; wherein the housing extends around the lateral side edges of the first and second substrate assemblies , around only a peripheral portion of the outer surface of the first substrate assembly , and around only a peripheral portion of the inner surface of the second substrate assembly . <EOS>