This Decisive Hour is a collection of letters and cablegrams from Shoghi Effendi to the North American Bahá’í community sent between 1932 and 1946. It was originally published under the title Messages to America.

As with Citadel of Faith the collection gives insight into the crises and victories faced by the American believers in the period covered by the letters, through the lens of guidance provided by the Guardian, and its value lies not only in the glimpse it gives into history but in the perspective it provides on the present, and the applicability of the principles identified to the issues of the current time.