Recent developments in quantum information need coherent manipulation of quantum states. Among solid-state systems, semiconductor quantum dots are promising candidates for realizing qubits. Important advantages are the three dimensional confinement leading to a discrete energy spectrum and the possible integration of dots in specific devices. In this presentation, I will show how with resonant optical pulses we can prepare and manipulate the states, and obtain single indistinguishable photons. I will also address the problem of interactions with the solid environment (phonons, fluctuating charges) of the quantum dots that may cause severe limitations in the quantum coherence.