We will address two major issues in the field of printed electronics: printing metallic conductive patterns on heat sensitive substrates, and obtaining transparent patterns and coatings for opto-electronic devices. New concepts for obtaining conductive patterns at low temperature will be presented, all based on spontaneous sintering of metallic nanoparticles caused due to removal of the ink stabilizer. The process can be performed with inks containing built-in sintering agent, or by sequential printing of the metallic ink and the sintering agent. A new method for fabrication of conductive transparent electrodes will be also described, based on spontaneous self-assembly of metallic nanoparticles into a grid pattern on plastic substrate, and on thin films of CNTs. Combining the printing with transparent patterns will be demonstrated in fabrication of a plastic electroluminescent device.