Putonghua

In practice it can be viewed as being identical to Mandarin Chinese. The theory behind putonghua is radicially different from the theory behind guoyu. Guoyu is exclusively based on the pronunciation of words from Beijing and Putonghua is influenced by non-Beijing pronunciations. However in practice the differences are small differences with Guoyu in:

1. tone.
2. transcription: Putonghua uses Pinyin.

Putonghua and guoyu refer to speech and hence the difference in the use of simplified characters and traditional characters is not usually considered to be a difference between these two concepts.