Jean-Paul Montagner is a pioneering and influential seismologist who has made fundamental contributions to seismology, especially for the study of Earth’s deep interior and dynamics through his work on seismic anisotropy. The birth of digital seismology that occurred in the late 1970s brought an evolution in global seismology, seismic tomography. While most leading seismologists of the time had challenged the problem assuming Earth is an isotropic elastic compound, Jean-Paul was not satisfied with this view. From his graduate student studies, he has been the advocate of the significance of seismic anisotropy in the mantle. His message is a simple one: Anisotropy is a first-order feature of the mantle heterogeneities and should be treated as such in tomography. By the late 1980s, together with colleagues, he had formulated the framework of how to solve the problem that is still used today in forefront research, and in the early 1990s, he presented the first global map of seismic anisotropy of the mantle. Since then, his message has been followed more and more by seismologists. Jean-Paul’s approach to the problem is not limited to seismology or scale. Earlier, he showed how to incorporate nonseismological information, such as crystal-scale anisotropy, as a constraint, which became a standard. The scheme to azimuthally average anisotropy elastic properties to give corresponding transversely isotropic ones is now sometimes referred to as “Montagner averaging” in the literature. The incorporation of geodynamic constraints has also set a new direction in research. Anisotropy tomography conducted by his group is applied from a global scale to various regional-scale important targets, including employment of observation data in the ocean. Findings made in these studies are numerous, delivering seeds for nextgeneration research. Jean-Paul’s contribution to seismology goes beyond mantle tomography. Much of his recent research focus is on pioneering research in the application of modern methodologies to important targets, such as seismic interferometry in the monitoring of a change in crustal anisotropy, time reversal in seismic source imaging, etc. He played a key role in the recent discovery of the earthquake-induced prompt gravity signal as a novel way of earthquake early warning. In addition, Jean-Paul has performed many administrative services for the science community. Among them, he has been a strong supporter and advocate for global digital seismic networks, especially for seafloor seismic observatories, which comprise the basis of the study of Earth’s interior. 

— Hitoshi Kawakatsu Earthquake Research Institute, The University of Tokyo Tokyo, Japan Institute of Earth Sciences, Academia Sinica Taipei, Taiwan