I think most Christians would say that temptation, in and of itself, is not sin. However, I came across a contrary view regarding temptation held by John Calvin. Calvin, who usually agrees with virtually anything Augustine says, takes a different view of temptation.
"Content to designate it with the term "weakness," he (Augustine) teaches that it becomes sin only when either act or consent follows the conceiving or apprehension of it, that is, when the will yields to the first strong inclination. We, on the other hand, deem it sin when man is tickled by any desire at all against the law of God. Indeed, we label "sin" that very depravity which begets in us desires of this sort" (Institutes III.III.10).
One possibility is that Calvin is being inconsistent. Perhaps in other places he argues that temptation, in and of itself, is not sin but then fails to be consistent in this passage. As it stands, this passage clearly indicates that temptation is sin. In fact, the nature that could possibly sin (i.e. depraved nature) is itself sin, according to Calvin.
That's an odd position to hold, in my opinion. What would make this opinion even more controversial is the implications it has for our Lord's Incarnation. I think the orthodox position is that our Lord was tempted, but did not sin. If Calvin argues that our Lord was tempted, then (based on this passage) he would also have to conclude that our Lord sinned in even being tempted. I seriously doubt Calvin would be comfortable with that conclusion (although, Calvin is comfortable with all kinds of positions that make most folks uncomfortable). So, assuming the above passage is his settled position, Calvin is not being consistent.
At any rate, what do you think. Is being tempted itself a sin?