Blockchain technology is evolving rapidly and has attracted concern not only in economics, but also has social, political and legal implications. Blockchain, referred to as Distributed Ledger Technology (DLT), makes any digital asset inalterable and transparent through the use of decentralization and cryptographic hashing. Specifically, the blockchain is a distributed database of records of all transactions that have been executed and shared among participating parties into the network. At the top layer of blockchain, there are applications that run on the network. These applications are called DApps. Decentralized application is an application which is built on a decentralized network that combines a smart contract and a user interface. DApps are currently developed and deployed on blockchain platforms like Ethereum, Eos, Tron, Cardano, Neo, Tezos. Τhe thesis focuses on decentralized applications, stating the need for them, their advantages and categorizing them in the above reported scopes. Especially types and core components of blockchain are analyzed. Also, decentralized applications are categorized in the paper as gaming, financing, socialization and referred to in the way they operate and the benefits of using them. Finally, I indicate my opinion regarding the concerns about using them and the reasons which they have not been massively adopted. On the other side, I exhibit the usefulness of decentralized applications and potential ways for their improvement regarding their adoption from a wider group of users.