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We determined the values of K_a for a wide range of host−guest complexes of cucurbit[n]uril (CB[n]), where n = 6−8, using ¹H NMR competition experiments referenced to absolute binding constants measured by UV/vis titration. We find that the larger homologuesCB[7] and CB[8]individually maintain the size, shape, and functional group selectivity that typifies the recognition behavior of CB[6]. The cavity of CB[7] is found to effectively host trimethylsilyl groups. Remarkably, the values of K_a for the interaction of CB[7] with adamantane derivatives 22−24 exceeds 10¹² M^-1! The high levels of selectivity observed for each CB[n] individually is also observed for the CB[n] family collectively. That is, the selectivities of CB[6], CB[7], and CB[8] toward a common guest can be remarkably large. For example, guests 1, 3, and 11 prefer CB[8] relative to CB[7] by factors greater than 10⁷, 10⁶, and 3000, respectively. Conversely …