The book deals with the legal regulation of interception of electronic communications in the Czech Republic and Slovakia. The book analyses legal grounding of interception of electronic communication conducted by police authorities in the regime of criminal procedure, by the police forces during fulfilment of their duties arising from the act No. 273/2008 Sb., on the Police of the Czech Republic and by the intelligence services in the course of their duties. In five chapters several topics are subsequently described: architecture of the legal regulation system of electronic communications interception, constitutional principles, authorization of relevant public bodies to access the interceptions, possibility of use of electronic communication data in judicial proceedings and exchange of intercepted electronic communication data between foreign countries. Slovak legal regulation is covered by the means of comparative remarks. The book also covers the topic of retention of traffic and location data by electronic communications operators and legal grounds for access to such data.