Tef (Eragrostis tef (Zucc.) Trotter) is a C4 annual cereal, common in Ethiopia, where it was presumably domesticated. Worldwide interest in tef cultivation and consumption has considerably increased in the last few decades because it is a gluten-free grain with high nutritional value. Here we report on the genetic diversity and heritability in a tef germplasm collection characterized in Israel. A total of 408 accessions of tef held in the Israel Gene Bank were grown in 2015 under common garden (screen-house) conditions for propagation and initial phenotyping. A diversity panel, consisting of 273 accessions representing the entire collection's range of phenotypic diversity, was assembled and evaluated in small field plots in 2016. Further evaluation was conducted in 2017, in single-plant field plots (to eliminate admixtures). A representative plant (plot) was selected from each accession grown in 2017 and its single seed descent progenies where grown in 2018 in single-plant plots. The collection exhibited a wide diversity for each of the measured phenotypic traits, across all four environments. High grain yield was associated in most cases with early flowering time, whereas higher biomass was associated with late flowering. Heritability estimates, calculated based on the 2017, 2018 data, varied between 0.11 for plant biomass and 0.75 for 1000 grain weight. This study shows that tef can successfully grow and produce under irrigated Mediterranean conditions. The wide diversity available in our germplasm collection can provide the foundations for breeding new tef cultivars that are better adapted to these conditions.