Transition metal complexes have emerged as promising candidates for applications in solid state electroluminescent devices. These materials serve as multifunctional chromophores, into which electrons and holes can be injected, migrate and recombine to produce light emission. Their device characteristics are dominated by the presence of mobile ions that redistribute under an applied field and assist charge injection. An efficiency of 10 lm/W –among the highest efficiencies in a single layer electroluminescent device– was recently demonstrated in an iridium complex. We present recent experimental results and discuss the issues that need to be addressed for these materials to succeed in display and lighting applications.