This is one of the best introductions to existentialism, which in my opinion is a huge achievement mostly because not many of that kind of compilations age well. We have here almost every crucial information about philosophical existentialism and nice explanation how phenomenology was a great contribution to it. This book is also written using clear language that can be also accessible to people that do not read many philosophical books and struggle with complicated analyses. I will really recommend this one if someone wants to understand why existentialism was such a big intellectual movement in Europe.
Existentialism is defined as a tradition of philosophical inquiry associated mainly with certain 19th and 20th-century European philosophers who, despite profound doctrinal differences, shared the belief that philosophical thinking begins with the human subject, not merely the thinking subject, but the acting, feeling, living human individual.
A good book if you are looking for an introduction into existentialist thought. There are areas where you find somewhat complex arguments, particularly with Heidegger and Sartre's ideas. But worth reading and written in a very accessible style.