Ferroelectric perovskite ceramics (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 were widely studied over the last 20 years, especially ceramics in the morphotropic phase boundary (x = 0.3–0.4). More recently a new interest focuses on single crystals of the same composition grown either by Bridgman or flux technique. Giant electromechanical factor k31, piezoelectric coefficient d31, and field-induced strain S3 were found (k31 > 0.85, d31 > 1000 pC/N, S > 1%) making them very attractive for non-resonant applications. For resonant applications, despite their medium mechanical factor Q31 these materials exhibit higher figure of merit Q31d31 than the best PZT (Q31d31 > 3 × 105 for crystal, and Q31d31 > 105 for the best PZT ceramics).However the origin of these outstanding properties is not well understood. The comparison between ceramics and crystal of the same composition (0.67PMN–0.33PT) towards the macroscopic properties was investigated. First the polarisability of materials was studied. The crystal shows an optimum poling electric field, which gives a maximum electromechanical coupling factor and piezoelectric charge d31. It is believed that this surprising behaviour is due to the domain and phase engineering.The temperature and electric field stability was investigated for ceramics and crystal for different crystallographic cuts. A discussion is presented on the mechanical losses which are especially unstable.