Pedro José Sebastião is a professor of experimental physics (Professor Associado com Agregação) in the Department of Physics at Instituto Superior Técnico, Universidade de Lisboa. Following the completion of his PhD thesis in 1993, which focused on molecular dynamics in liquid crystals with peculiar polymorphisms using proton nuclear magnetic resonance (NMR) relaxometry, he has investigated a large number of condensed matter systems using NMR. His goal has been to understand the interdependence between molecular organization and molecular dynamics. Since NMR relaxometry can provide information about molecular motions in different time and length scales, P.J. Sebastião has always been concerned with being able to cover a broad range of NMR frequencies from hundreds of MHz to kHz in NMR relaxometry studies. Fast Field-Cycling relaxometry has proved to be crucial in obtaining information below the MHz range and, over the past 30 years, he has devoted some of his efforts to the development of new, more efficient, FFC NMR relaxometry equipment. P.J. Sebastião is the author of the fitteia.org site, which is devoted to model fitting and data analysis in physics and engineering and has been well received by students from different continents. In his research activities, P.J. Sebastião has investigated molecular order and dynamics in liquid crystals (i.e. materials that present thermodynamically stable phases between the isotropic and solid phases, where properties like fluidity, characteristic of liquids, are found simultaneously with properties characteristic of crystals, like birefringence), dendrimers, polymers (e.g. in-bulk, membranes, nano composite systems), electrolytes (e.g. pure ionic liquids, polymer electrolytes, salt solutions), heterogeneous systems (e.g. liquid crystals in nano-porous glasses, small molecules dispersed in porous membranes). As examples, in the liquid crystals area, he has investigated blue phases, nematic phases (N, N*, Ntb), smectic phases (A, Ad, A2, C, B, chiral phases C* (e.g. ferroelectric, anti-ferroelectric), TGBA*, and TGBC*). All of these systems present different types of molecular organization that affect molecular dynamics, and the development of relaxation models has proved to be essential.