Molecular Nonlinear Optics, an otherwise well established domain, is currently revisiting and shaking its foundations,
objectives and methods, in the frame of ongoing conceptual as well as methodological revivals. These are based on
correlated advances in chemistry and physics, entailing spectacular advances in the new playground of multiphoton bio-imaging.
For chemistry, we chose to review and highlight a comprehensive multipolar template approach will helps
rationalize and generalize molecular design rules, with current emphasis on multi-functionality and the nano-scale. In
consistence with advances in chemistry, we emphasize for physics the domain of nonlinear micro- and nano-photonics,
in particular with respect to active nonlinear coupling schemes, based on interference of multi-photon absorption
pathways. It permits to encode nonlinear information or guide the displacement of molecular or nano-scale objects by
adequate laser illumination. Building-up on these advances and more, advanced bio-imaging methods such as based on
phase and polarization resolved nonlinear schemes, are currently opening-up new windows onto cellular structures and
mechanisms, with the potential towards unprecedented spatial resolution.