We study the conservative as well as the dissipative quanta] dynamics in a harmonically driven, quartic double-well potential. In the deep quanta] regime, we find coherent modifications of tunneling, including its complete suppression. In the semiclassical regime of the conservative system, the dynamics is dominated by the interplay of tunneling and chaotic diffusion. A strong correlation exists between the tunnel splittings and the overlaps of the associated doublet states with the chaotic layer. With weak dissipation, remnants of coherent behaviour occur as transients, such as the tunneling between symmetry-related pairs of limit cycles. The coherent suppression of tunneling observed in the conservative case is stabilized by weak incoherence.The quanta] stationary states are broadened anisotropica]ly due to quantum noise, as compared to the corresponding classical attractors.