The purpose of the present thesis is to compare eight free online dictionaries which you first come across on the World Wide Web if you use Google to search for free online dictionaries. The result of my search is very varied, these dictionaries differ in several aspects as some of them are very simple while the others are quite complex. However, before I start the comparison I would like to define lexicography, outline the requirements that dictionaries should meet, introduce the different types of dictionaries highlighting the main characteristic features of bilingual and monolingual ones contrasting the latter with encyclopedias, talk about the microstructure and macrostructure of dictionaries and give a brief history of dictionaries in general and online dictionaries in particular. At the end of my thesis I will draw a conclusion about the usefulness of the searched free online dictionaries.