A mechanism is described for the development of strange nonchaotic att
ractors from two-frequency quasiperiodic attractors in quasiperiodical
ly driven maps. This mechanism is intimately tied to the phenomenon of
torus-doubling. The transition to strange nonchaotic behavior occurs
when a period-doubled torus collides with its unstable parent torus. A
s the collision is approached, the period-doubled torus becomes extrem
ely wrinkled, ultimately becoming fractal at the collision. The Lyapun
ov exponent remains negative through the collision. These collisions a
re shown to be a new type of attractor merging crisis; the new feature
is the possibility of nonchaotic attractors taking part in the crisis
. This mechanism is illustrated via numerical and analytical studies o
f a quasiperiodically driven logistic map.