M2M is rapidly growing and since its early days different "standard" protocols have emerged (e.g. OMA-DM, TR-069, MQTT, ...) or are emerging (e.g. CoAP or Lightweight M2M). Understanding which protocol to use for which application can be intimidating, therefore we propose to give an overview of these protocols to help you understand their goals and characteristics. We will give a status of the availaible open source implementations in the Eclipse M2M ecosystem, with projects such as Paho, Mihini and Ponte. We'll present common M2M use cases and why they usually require more than just one protocol, and discuss whether the current portfolio of available M2M protocols possibly allows to forge "one protocol to rule them all".