Hrvoje Tkalčić is a geophysicist who has made fundamental contributions to the study of the Earth’s interior, notably the Inner Core using an innovative approach to detect shear wave propagation and so demonstrate the solidity of the innermost part of the Earth. His breakthrough work in the understanding of the seismic correlation wavefield opened the way for global and planetary seismology to illuminate the interiors of the Earth and other planets. He has also made significant contributions to seismic source studies, including tectonic and volcanic earthquakes, explosions and marsquakes, and to the development of analysis techniques for seismograms with effective treatment of uncertainty in matching observations and theoretical predictions.