Taqiyya: Islamic doctrine of deceit to defend and promote Islam

Taqiyya is "concealing or disguising one's beliefs, convictions, ideas, feelings, opinions, and/or strategies at a time of imminent danger, whether now or later in time, to save oneself from physical and/or mental injury."  A one-word translation would be "dissimulation." [4]   Taqiyya is one of the principle tools of "stealth jihad."
Most westerners are acquainted with lying that characterize many politicians, salesman and folks of low character, generally.  But we are not readily willing to accept the concept of lying being associated with a religion.  Sadly, taqiyya is integral to Islam.  That is what makes its use by Muslims against westerners so effective:  We don't readily realize or admit such practice exists. 
Taqiyya may be employed for any purpose whereby "any end justifies the means."  Taqiyya is closely related to the command of  "Kithman":  Hiding the truth; deliberately concealing one's beliefs.
Practically, taqiyya is any  form of lying, deceit, misleading, half-truths or related practices condoned by Islamic doctrine to further the growth of Islam or to protect the individual from harm.  Taqiyya is one of the reasons we are "surprised" by acts of violence or terror from those previously considered to be "moderate" Muslims.  See also "sudden Jihad syndrome."  Joel Richardson has wrritten a piece worth reading about "Understanding the Dishonesty and Deceit of Islam."
The Taqiyya doctrine is based on the following verse from Qur'an 3:28: "Let not the believers take for friends or helpers unbelievers rather than believers. If any do that, in nothing will there be help from Allah; except by way of precaution, that ye may guard yourselves from them". Sunni commentator Ibn Kathir explained that "believers that fear for their safety from the unbelievers... are allowed to show friendship to the unbelievers outwardly, but never inwardly".

According to the Shia scholar Muhammad Husain Jafari Sahiwal, Shi'ism would not have spread if it wasn't for taqiyya. (Referring to instances where Shiites have been ruthlessly persecuted by the Sunni political elite, during the Umayyad and Abbasid empires.[6]   Today, both Sunni and Shia sects of Islam promote and widely employ taqiyya.

Robert Spencer explains how Taqiyya changes the rules of war here.

Can a Tiger change its stripes?  Or a scorpion its sting?

Consequences of Taqiyya in the West

"The principle of sanctioning lying for the cause of Islam bears grave implications in matters relating to the spread of the religion of Islam in the West.  Muslim activists employ deceptive tactics in their attempts to polish Islam's image and make it more attractive to prospective converts" Abdullh Al Araby, "Lying in Islam
...and to protect it from government and public scrutiny.
"I have personally witnessed this dynamic [the practice of "taqiyya"] to the point of utter exhaustion.  And equally frustrating is the fact that so many Christians, due to either a lack of knowledge or simply not wanting to appear contentious, allow the deception to flow unchecked.  When America witnessed numerous so-called modeate Muslims make speeches to defend the benign nature of "the Religion of Peace," after 9/11, for instance, many of these speakers knowingly misrepresented the true nature of Islam.  Many have been documented speaking in far more aggessive terms in private meetings with other Muslims. 
"These Muslims, posing as "moderates," justified their misrepresentations of Islam because in their minds, they were protecting Islam, and thus American Muslims, from "harm."  It was "damage control" in its truest form. 
"Christians, Americans, and unfortunately, even much of the political leadership, either desperately want to believe the best of people in order to comfort themselves in times of great uncertainty, or through the inevitable dumbing down of the West through the constant hammering of moral relativity and politcal correctness, bought much of this deception - hook, line, and sinker.  Those few bold enough to speak the truth regarding the true nature of Islam were viewed as intolerant or hateful or both.  This is the pattern followed whenever Islam carries out a great evil.  Pay attention and you will see it again and again."
 Excerpt from Joel Richardson's "Islamic Anti-Christ", pages 159-160