Chapters 5 and 6 describes the “second wave” of the AIDS epidemic among gay men in the 90s. Evidence showed that gay men were using condoms at historically high levels, in some studies up to 60% of the time. But epidemiological studies and mathematical models of the epidemic began to indicate that that was not high enough to bring the epidemic below the tipping point, primarily because prevalence was already so high that any failures to use condoms had a high chance of leading to a new infection. Rotello also presents evidence that while condoms are highly effective for individuals, the dramatic collective drop in new infections in the late 1980s had been due less to condoms than to the phenomenon of ‘saturation,” in which once 50-60% of gay men were infected, new infections had to decline until a new cohort of young uninfected men became sexually active.