Note: Full citations for all works mentioned in this essay are included at the end of this article.

Even before the dust had settled on Ground Zero and the fires were extinguished at the Pentagon, a host of writers had furrowed their brows and fired up their PCs to set about explaining September 11. On the eve of the fourth anniversary of 9/11, they are still writing. The cumulative result has been literally hundreds of books designed to satisfy the intense need of Americans to understand the recent past and guide them away from future peril.

Not surprisingly, the quality of the early books is uneven, particularly as many are the work of under-tutored journalists following the siren call of their bank accounts. Over time, writing and research on 9/11 and Islamist terrorism have improved, but a want of analytical quality remains. While genuine authorities on the Middle East have by now brought their years of experience to bear, they have also brought in train their prejudices--about the United States, Israel, Islam and myriad related topics. Policymakers from the Clinton and Bush Administrations, too, have parlayed their access into books, and the result has been a general propensity to blame everyone but themselves for the attacks. If this were not reason enough to be wary (and weary) of the extant literature, obvious partisans have also piled on, seeing as their sacred duty either the defense or the excoriation of the current Administration.

The upshot is that, of all the tomes on terrorism, al-Qaeda, Osama bin Laden, radical Islam, the assault on America and the war on terror that have appeared in the past four years, only a few dozen merit serious consideration. The rest qualify as pulp non-fiction.

The serious works we do have help us in different ways. Some books are important because their contrarian views challenge us and make us think. Others are important simply because, for one reason or another, they have become popular and have thus shaped public debates. Still others are useful because they provide real data, enough in some cases to enable readers to make up their own minds. And thankfully, a few books provide genuine insight into the three issues that have consumed Americans, and of course many others, since 9/11: Who precisely is the enemy? What motivates him? What must be done to stop him?

Now a book, as is well understood, is only as useful as its reader is needful and attentive. Lay readers must take great care, for while they are liable to benefit from a serious book more than an expert, they are at the same time more vulnerable...