Under UK REACH, as a registrant, you must collect information on the properties and uses of the substances you manufacture or import above one tonne a year. You should also assess the hazards of the substance and any potential risks presented by its uses.
Registration applies to substances on their own, substances in mixtures (formulated products) and in certain limited cases to substances in articles. Chemical substances that are already regulated by other legislations such as medicines, or radioactive substances are partially or completely exempted from REACH requirements.
Under UK REACH, the principle of "one substance, one registration" has been retained. This means that manufacturers and importers of the same substance should be part of a 'joint registration'. This is to minimise the use of animal testing and to allow the costs of generating the registration data to be shared. For new substance registration a fee is usually charged.
If there is more than one registrant for a substance, co-registrants should agree between themselves who the 'lead registrant' will be.
If you have not previously manufactured or imported a particular substance, you will need to consider if it requires registration under UK REACH.