The slope and zero-point of the unevolved main sequence as a function of metallicity are investigated using a homogeneous catalog of nearby field stars with absolute magnitudes defined with revised Hipparcos parallaxes, Tycho-2 photometry, and precise metallicities from high-dispersion spectroscopy. (B − V ) -temperature relations are derived from 1746 stars between [Fe/H] = −0.5 and +0.6 and 372 stars within 0.05 dex of solar abundance; for T e = 5770 K, the solar color is B − V = 0.652 ± 0.002 (s.e.m.). From over 500 cool dwarfs between [Fe/H] = −0.5 and +0.5, ∆(B − V )/∆[Fe/H] at fixed M V = 0.213 ± 0.005, with a very weak dependence upon the adopted main sequence slope with B − V at a given [Fe/H]. At Hyades metallicity this translates into ∆M V /∆[Fe/H] at fixed B − V = 0.98 ± 0.02, midway between the range of values empirically derived from smaller and/or less homogenous samples and model isochrones. From field stars of similar metallicity, the Hyades ([Fe/H] = +0.13) with no reddening has (m − M ) 0 = 3.33 ± 0.02 and M67, with E(B − V ) = 0.041, A V = 3.1E(B − V ), and [Fe/H] = 0.00, has (m − M ) 0 = 9.71 ± 0.02 (s.e.m), where the errors quoted refer to internal errors alone. At the extreme end of the age and metallicity scale, with E(B − V ) = 0.125 ± 0.025 and [Fe/H] = +0.39 ± 0.06, comparison of the fiducial relation for NGC 6791 to 19 field stars with (B − V ) above 0.90 and [Fe/H] = +0.25 or higher, adjusted to the metallicity of NGC 6791, leads to (m − M ) 0 = 13.07 ± 0.09, internal and systematic errors included.