Many RFID technologies are proprietary and use proprietary technologies and protocols defined many years ago when RFID was first used in simple applications such as access control. Recently, ISO standards have been defined for different frequency and transponder technologies. These ISO standards can define modulation techniques and communication protocols, but typically the memory size, security features (encryption, etc.) are still proprietary to one manufacturer or another manufacturer.  

Examples of RFID standards are:

ISO11784 / 785, 134kHz “Animal Label”
ISO14443A, 13.56MHz Mifare card/label
ISO15693, 13.56MHz ICODE card/label
ISO18000-6B / 6C, 850-950MHz UHF Gen1 / 2 EPC card / label
Many popular passive tag types are widely used and considered “standard”, but are actually proprietary technologies from one company or another. In many cases, this technology has been licensed to other manufacturers to allow for wider use.