Rabbi Moshe Becker
Mosaica Press / 126 pp
A project whose proceeds are being put to tzedaka, the Kippah is an absolutely lovely presentation of everything one needs to know about the importance of wearing a Kippah. The book's goal is to inspire those "on the fence" to begin wearing a Kippah and to further encourage those who already do.
Every chapter presents the Kippah from a different aspect of rabbinic literature, citing the original sources in both Hebrew and English, and then elaborating upon them in an especially gentle, clear, and thorough manner. For example, chapter one cites the Talmudic sources, chapter two cites sources in the rishonim, chapter three cites the relevant halachic sources, and so on.
The book is small-size, very easy reading, and handy to have as a permanent reference guide. It is definitely required reading for your friends and neighbors who may not yet be wearing a Kippah and are in need some inspiration to begin doing so.
N.B. I strongly disagree with the author's theory on p.91 that wearing a baseball cap in place of a kippa may be problematic according to the Mishna Berura due to concerns of ma'arit ayin, similar to the concerns with wearing a tupee in place of a kippa. There is no source to suggest that there is a need to appear Jewish by means of one's head covering. v'kan ain hamakom l'ha'arich