Pre-registration is only for companies planning to register phase-in (existing) substances. After pre-registration, potential registrants of the same substance can find each other's contact details in REACH-IT, so they can get in contact to agree on the sameness of their substance, form a substance information exchange forum (SIEF), share data and submit a registration dossier jointly.


Companies need to pre-register if they want to benefit from the extended registration deadlines foreseen for phase-in substances.
The main pre-registration period was between 1 June and 1 December 2008.
Companies starting to manufacture or import a phase-in substance in amounts of one tonne per year or more after 1 December 2008 can submit a late pre-registration and still benefit from the extended deadlines. Producers and importers of articles with an intended release of a phase-in substance can also submit a late pre-registration.
Late pre-registrations have to be submitted:
  • within six months after exceeding the one tonne per year threshold; and 
  • no later than 12 months before the relevant registration deadline.
Therefore, late pre-registrations can be submitted until 31 May 2017 for substances that need to be registered by 31 May 2018. The 2018 deadline concerns phase-in substances manufactured or imported in quantities below 100 tonnes per year, which are not cancerogenic, mutagenic or reprotoxic (CMR) category 1A or 1B. Other phase-in substances can no longer be pre-registered.
For substances which cannot be pre-registered anymore, or substances for which the company decides not to pre-register, potential registrants need to submit an inquiry to ECHA before registering.


Companies who have pre-registered a substance will automatically become listed in a  REACH-IT forum called a pre-SIEF . These companies need to agree on the identity of the substance they will register.
Those companies that agree that their substance is the same, form a substance information exchange forum (SIEF). Companies with a later registration deadline can become members of the SIEF at a later time.
As a result of the discussions on the substance identity, some pre-SIEFs for complex substances might merge or split before forming a SIEF. In both cases, the decision needs to be clearly documented. 


Substance information exchange forums (SIEF)
Companies that intend to register the same phase-in substance will form or join a substance information exchange forum (SIEF). They need to share data on the intrinsic properties of the substance, and work together to identify and carry out additional studies or submit testing proposals when needed. In particular, they have the obligation to share all test data on vertebrate animals. The members of the SIEF should also agree on the classification and labelling of the substance.
The work of a SIEF leads to one joint submission for each substance, therefore reducing costs for the registrants and avoiding unnecessary animal testing.
Participating in a SIEF is a legal obligation for all registrants of pre-registered phase-in substances. 
In addition to potential registrants,  also downstream users and any person or organisation holding data relevant to a phase-in substance can participate in the SIEF, if they have identified themselves as a data holder and are willing to share their information.
SIEFs have no prescribed legal form and they are independently managed by industry. ECHA is not involved in their operations.


Lead registrants and member registrants
SIEF participants need to appoint a lead registrant who must act with the agreement of the other co-registrants and submit the lead dossier of the joint submission. The lead registrant may coordinate the activities within the SIEF, but other arrangements can also be agreed. REACH does not specify rules on how the lead registrant should be selected.
A lead dossier includes the substance identifiers, the classification and labelling of the substance, and all the needed (robust) study summaries and proposals for further testing. The registrants need to decide if the lead will submit the guidance on safe use of the substance and the chemical safety report on behalf of the members, or if it will be included in the members' dossiers. The lead dossier needs to be submitted first, before the members can submit theirs.
Member registrants afterwards submit dossiers containing only information specific to their company and their substance, for example, information about the impurity profile of their substance, their identified uses and their production volumes. These submissions do not need to include the information already provided by the lead registrant.