Below are books I recommend on Yemen, divided into four categories based on nothing other than my own biases.

General/Accessible:

Yemen: Travels in Dictionary Land, Tim Mackintosh-Smith
(US Title: Yemen: The Unknown Arabia)
My all-time favorite book on Yemen

Specialist/Scholarly

A History of Modern Yemen, Paul Dresch
A Dense but highly informative read on the history of 20th Century Yemen


Revival and Reform in Islam: The Legacy of Muhammad al-Shawkani, Bernard Haykel
An excellent history of some of the theological underpinnings of modern Yemen.

A Tribal Order, Shelagh Weir
Excellent book that is focused on tribes and politics in Sa'dah, not on the Huthi conflict

San'a: An Arabian Islamic City, RB Serjeant and Ronald Lewcock eds.
The Holy Grail of Yemen Books

Mawla'i Level (if you don't get the reference stay away from this section)

Tribes, Government and History in Yemen
, Paul Dresch
Excellent source of information that challenges the reader

Ma'sah waq al-waq, Muhammad Mahmud al-Zubayri
(The Tragedy of Waq al-waq)
One of the handful of founding sources for this blog

Reference Level

Mu'ajim al-Buldan wa al-qaba'il al-yamaniyya, Ibrahim Ahmad al-Maqhafi
Yemeni Geographical and Tribal dictionary - indispensable

Al-mausu'a al-yamaniyya, Dar al-Afif (2nd ed. 4 vols)
Yemeni Encyclopedia - sits next to my desk