We present observations of the interstellar interloper 1I/2017 U1 ('Oumuamua) taken during its 2017 October flyby of Earth. The optical colors B - V = 0.70 +/- 0.06, V - R = 0.45 +/- 0.05, overlap those of the D-type Jovian Trojan asteroids and are incompatible with the ultrared objects that are abundant in the Kuiper Belt. With a mean absolute magnitude H-V = 22.95 and assuming a geometric albedo p(V) = 0.1, we find an average radius of 55 m. No coma is apparent; we deduce a limit to the dust mass production rate of only similar to 2 x 10(-4) kg s(-1), ruling out the existence of exposed ice covering more than a few m(2) of the surface. Volatiles in this body, if they exist, must lie beneath an involatile surface mantle greater than or similar to 0.5 m thick, perhaps a product of prolonged cosmic-ray processing in the interstellar medium. The light curve range is unusually large at similar to 2.0 +/- 0.2 mag. Interpreted as a rotational light curve the body has axis ratio >= 6.3(-1.1)(+1.3):1 and semi-axes similar to 230 m x 35 m. A greater than or similar to 6:1 axis ratio is extreme relative to most small solar system asteroids and suggests that albedo variations may additionally contribute to the variability. The light curve is consistent with a two-peaked period similar to 8.26 hr, but the period is non-unique as a result of aliasing in the data. Except for its unusually elongated shape, 1I/2017 U1 is a physically unremarkable, sub-kilometer, slightly red, rotating object from another planetary system. The steady-state population of similar, similar to 100 m scale interstellar objects inside the orbit of Neptune is similar to 10(4), each with a residence time of similar to 10 years.