  We outline our methods for obtaining high precision mass profiles, combining
independent weak-lensing distortion, magnification, and strong-lensing
measurements. For massive clusters the strong and weak lensing regimes
contribute equal logarithmic coverage of the radial profile. The utility of
high-quality data is limited by the cosmic noise from large scale structure
along the line of sight. This noise is overcome when stacking clusters, as too
are the effects of cluster asphericity and substructure, permitting a stringent
test of theoretical models. We derive a mean radial mass profile of four
similar mass clusters of high-quality HST and Subaru images, in the range
R=40kpc/h to 2800kpc/h, where the inner radial boundary is sufficiently large
to avoid smoothing from miscentering effects. The stacked mass profile is
detected at 58-sigma significance over the entire radial range, with the
contribution from the cosmic noise included. We show that the projected mass
profile has a continuously steepening gradient out to beyond the virial radius,
in remarkably good agreement with the standard Navarro-Frenk-White form
predicted for the family of CDM-dominated halos in gravitational equilibrium.
The central slope is constrained to lie in the range,
-dln{\rho}/dln{r}=0.89^{+0.27}_{-0.39}. The mean concentration is
c_{vir}=7.68^{+0.42}_{-0.40} (at a mean virial mass 1.54^{+0.11}_{-0.10}\times
10^{15} M_{sun}/h), which is high for relaxed, high-mass clusters, but
consistent with LCDM when a sizable projection bias estimated from N-body
simulations is considered. This possible tension will be more definitively
explored with new cluster surveys, such as CLASH, LoCuSS, Subaru HSC, and
XXM-XXL, to construct the c-M relation over a wider mass range.
