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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$\pm$0.06, V-R = 0.45$\pm$0.05, overlap those of the D-type Jovian Trojanasteroids and are incompatible with the ultrared objects which are abundant inthe Kuiper belt. With a mean absolute magnitude $H_V$ = 22.95 and assuming ageometric albedo $p_V$ = 0.1, we find an average radius of 55 m. No coma isapparent; we deduce a limit to the dust mass production rate of only $\sim$2$\times$10$^{-4}$ kg s$^{-1}$, ruling out the existence of exposed icecovering more than a few m$^2$ of the surface. Volatiles in this body, if theyexist, must lie beneath an involatile surface mantle $\gtrsim$0.5 m thick,perhaps a product of prolonged cosmic ray processing in the interstellarmedium. The lightcurve range is unusually large at $\sim$2.0$\pm$0.2magnitudes. Interpreted as a rotational lightcurve the body has semi-axes$\sim$230 m $\times$ 35 m. A $\sim$6:1 axis ratio is extreme relative to mostsmall solar system asteroids and suggests that albedo variations mayadditionally contribute to the variability. The lightcurve is consistent with atwo-peaked period $\sim$8.26 hr but the period is non-unique as a result ofaliasing in the data. Except for its unusually elongated shape, 1I/2017 U1 is aphysically unremarkable, sub-kilometer, slightly red, rotating object fromanother planetary system. The steady-state population of similar, $\sim$100 mscale interstellar objects inside the orbit of Neptune is $\sim$10$^4$, eachwith a residence time $\sim$10 yr.

Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes