A modular reactor comprising: at least first, second and third microstructure modules (12a-12c) each fluidically connected in successive order for fluid communication from one to the next, each of the first, second and third modules comprising: at least a first internal fluid passage, an external surface comprising an entrance side and an exit side opposite the entrance side, an entrance port extending through the entrance side of the module (12a-12c) to the first internal fluid passage, an exit port extending from the first internal fluid passage through the exit side, and a first edge and a second edge opposite the first edge, the first and second edges (26, 28) extending from the entrance side to the exit side, wherein, for each of the first, second and third modules (12a-12c), the entrance port and the exit port are positioned nearer to the first edge of the module (12a-12c) than to the second edge, and wherein the exit side of the first module faces the entrance side of the second module with the exit port concentric with or offset a specified distance from the entrance port of the second module, and wherein the exit side of the second module faces the entrance side of the third module with the exit port of the second module concentric with or offset the specified distance from the entrance port of the third module, and the first edges of the first, second and third modules (12a-12c) are aligned, and a first fluid connector extends from the exit port of the first module to the entrance port of the second module, and a second fluid connector extends from the exit port of the second module to the entrance port of the third module, and wherein the modular reactor further comprises an extended structural support member and wherein each microstructure module (12a-12j) is independently supported on the extended member by a respective connecting support structure adjustable in at least two linear displacement degrees of freedom (44, 46), one parallel to the direction of the long direction of the extended member and one perpendicular to the long direction of the extended member. at least a first internal fluid passage, an external surface comprising an entrance side and an exit side opposite the entrance side, an entrance port extending through the entrance side of the module (12a-12c) to the first internal fluid passage, an exit port extending from the first internal fluid passage through the exit side, and a first edge and a second edge opposite the first edge, the first and second edges (26, 28) extending from the entrance side to the exit side, wherein, for each of the first, second and third modules (12a-12c), the entrance port and the exit port are positioned nearer to the first edge of the module (12a-12c) than to the second edge, and wherein the exit side of the first module faces the entrance side of the second module with the exit port concentric with or offset a specified distance from the entrance port of the second module, and wherein the exit side of the second module faces the entrance side of the third module with the exit port of the second module concentric with or offset the specified distance from the entrance port of the third module, and the first edges of the first, second and third modules (12a-12c) are aligned, and a first fluid connector extends from the exit port of the first module to the entrance port of the second module, and a second fluid connector extends from the exit port of the second module to the entrance port of the third module, and wherein the modular reactor further comprises an extended structural support member and wherein each microstructure module (12a-12j) is independently supported on the extended member by a respective connecting support structure adjustable in at least two linear displacement degrees of freedom (44, 46), one parallel to the direction of the long direction of the extended member and one perpendicular to the long direction of the extended member.