What are the so-called flexible mechanisms?

Within the Kyoto Protocol a number of so-called flexible mechanisms were introduced. These are emissions trading, the clean development mechanism and joint implementation: Emissions trading The targets of industrialised nations with reduction commitments 2008 – 2012 in the framework of the Kyoto Protocol are defined as allowed emissions. These allowed emissions are divided into assigned amount units (AAU), each equivalent to 1 ton of CO2-eq. States who do not use all of their AAUs, can sell these to states who require more than the AAUs allocated them. Clean development mechanism (CDM) Under the clean development mechanism, projects that achieve emissions reductions can be implemented in non-annex B states. For every ton of CO2 reduced or avoided, a certified emissions reduction (CER) unit is generated. CERs can be traded and used for compliance with Kyoto targets by annex B states, or companies in the framework of the EU-ETS. Joint Implementation (JI) Under joint implementation, annex B states can implement projects, which achieve emissions reductions in other annex B states. These projects generate so-called emission reduction units (ERU) each also equivalent to one ton of CO2. These can also be used for compliance with targets in the framework of the Kyoto Protocol.
The idea behind JI, is to give annex B states flexible and cost efficient means of compliance and to boost investments and technology transfer between annex B states.