High-quality scientific research starts with detailed literature search. An average scientist reads ~200 articles per year. Over 100.000 scientific journals exist in the world, so it would be reasonable to limit the search by using only the most relevant journals. The Bradford law and the Pareto principle stipulate that the most relevant scientific information can be found in ~20 % of the published scientific literature. The role of the Web of Science (Core Collection) WoS (CC) is to index the most recognized scientific journals. Today, in WoS (CC) covers more than 12800 journals in three indexes of scientific literature (natural sciences, social sciences and art and humanities). Up to 5000 titles would be selected to form the newly established ESCI index which is also the part of the core collection. Since 50 years, WoS has become an indispensable tool in the search and evaluation of scientific information. The article provides information about the Web of Science platform content and analyses Ukrainian journals indexed in WoS Core Collection in 1997—2016.