Mainly Blockchain is classified in 3 types: –

(1) Public

(2) Private

(3) Consortium 

(1) Public
Public Blockchains have ledger visible to everyone on the internet and anyone can verify and add a block of transactions to block chain.

(2) Private
Private blockchains allow only specific people in the organisation to verify and add transaction blocks but everyone on the internet are allowed to view the ledger.

(3) Consortium
Consortium can be considered as combination of both Public and Private Blockchain. Here, only a group of organisation (such as banks) can verify and add transactions but the ledger can open or restricted to selected groups.