As the construction continued on the International Space Station (ISS), STS-118 Astronaut Dave Williams, representing the Canadian Space Agency, participated in the fourth and final session of Extra Vehicular Activity (EVA). During the 5 hour space walk, Williams and Expedition 15 engineer Clay Anderson (out of frame) installed the External Wireless Instrumentation System Antenna, attached a stand for the shuttle robotic arm extension boom, and retrieved the two Materials International Space Station Experiments (MISSE) for return to Earth. MISSE collects information on how different materials weather in the environment of space.

View of Expedition 15 Flight Engineer (FE-2), Clayton Anderson, working to install External Wireless Instrumentation System (EWIS) antennas on the exterior of the U.S. Laboratory/Destiny. Photo taken during the fourth session of Extravehicular Activity (EVA 4) for STS-118 / Expedition 15 joint operations.

S118-E-09157 (18 Aug. 2007) --- Astronaut Dave Williams, STS-118 mission specialist representing the Canadian Space Agency, participates in the mission's fourth and final session of extravehicular activity (EVA) as construction and maintenance continue on the International Space Station. During the 5-hour spacewalk, Williams and astronaut Clay Anderson (out of frame), Expedition 15 flight engineer, installed the External Wireless Instrumentation System antenna, attached a stand for the shuttle's robotic arm extension boom and retrieved the two Materials International Space Station Experiments (MISSE) to be brought back on the shuttle.

S118-E-09158 (18 Aug. 2007) --- Astronaut Dave Williams, STS-118 mission specialist representing the Canadian Space Agency, participates in the mission's fourth and final session of extravehicular activity (EVA) as construction and maintenance continue on the International Space Station. During the 5-hour spacewalk, Williams and astronaut Clay Anderson (out of frame), Expedition 15 flight engineer, installed the External Wireless Instrumentation System antenna, attached a stand for the shuttle's robotic arm extension boom and retrieved the two Materials International Space Station Experiments (MISSE) to be brought back on the shuttle.

ISS015-E-23053 (18 Aug. 2007) --- Astronaut Dave Williams, STS-118 mission specialist representing the Canadian Space Agency, participates in the mission's fourth and final session of extravehicular activity (EVA) as construction and maintenance continue on the International Space Station. During the 5-hour spacewalk, Williams and astronaut Clay Anderson (out of frame), Expedition 15 flight engineer, installed the External Wireless Instrumentation System antenna, attached a stand for the shuttle's robotic arm extension boom and retrieved the two Materials International Space Station Experiments (MISSE) to be brought back on the shuttle.

S118-E-09207 (18 Aug. 2007) --- Astronaut Dave Williams, STS-118 mission specialist representing the Canadian Space Agency, participates in the mission's fourth and final session of extravehicular activity (EVA) as construction and maintenance continue on the International Space Station. During the 5-hour spacewalk, Williams and astronaut Clay Anderson (out of frame), Expedition 15 flight engineer, installed the External Wireless Instrumentation System antenna, attached a stand for the shuttle's robotic arm extension boom and retrieved the two Materials International Space Station Experiments (MISSE) to be brought back on the shuttle.

S118-E-09144 (18 Aug. 2007) --- Astronauts Clay Anderson, Expedition 15 flight engineer, and Dave Williams (out of frame), STS-118 mission specialist representing the Canadian Space Agency, participate in the mission's fourth and final session of extravehicular activity (EVA) as construction and maintenance continue on the International Space Station. During the 5-hour spacewalk, Anderson and Williams installed the External Wireless Instrumentation System antenna, attached a stand for the shuttle's robotic arm extension boom and retrieved the two Materials International Space Station Experiments (MISSE) to be brought back on the shuttle.