New peroxide-free, amine-free, and phosphine-free redox free radical polymerization (RFRP) initiating systems comprising remarkably stable (i) metal acetylacetonates (Mn(acac)(3), Cu(acac)(2)) and (ii) carbonyl compounds bearing labile hydrogen in the alpha-position are presented for polymerization initiation under mild conditions (under air, at room temperature, nonpurified monomers). The systems proposed in this work are competitive or even outranked the well-known peroxide-based RFRP reference in several criteria: (i) toxicity, (ii) stability, (iii) surface curing, (iv) overall double-bond conversions, and (v) workability of the RFRP mixture (longer gel times are now possible). Radical initiating reactions are studied using many complementary experimental/theoretical techniques: optical pyrometry, thermal imaging, Raman confocal microscopy, electron spin resonance (ESR), ESR spin trapping (ESR-ST), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), density functional theory (DFT), simulations of bond dissociation energies (BDE), reaction enthalpies, and DFT simulations of seven unknown ESR-ST adducts. A full consistent picture of the chemical mechanisms involved in these new redox systems is provided.