This article is not here to regurgitate information you find all over the web regarding RoHS, but it is the aim of this article to summarize and simplify the main points of the Hazardous Substances Directive.
The Restriction of Hazardous Substances Directive (otherwise known as RoHS) is an EU directive which sets limits on the amount of certain hazardous chemicals such as Mercury, Cadmium and Lead (along with a lot more) that can be present in electrical equipment sold within the EU. Like the WEEE directive (more information here), it has been devised by the EU Commission to serve as a template for individual country's implementation as law.
The EU directive was created in 2003 and became UK law in February 2008. The main things within the law are as follows:
Producers shall ensure that new electrical and electronic equipment put on the market on or after 1st February 2008 does not contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls or polybrominated diphenyl ethers in quantities exceeding the following maximum concentration value levels—(a) 0.1% by weight in homogeneous materials for lead;
(b) 0.1% by weight in homogeneous materials for mercury;
(c) 0.1% by weight in homogeneous materials for hexavalent chromium;
(d) 0.1% by weight in homogeneous materials for polybrominated biphenyls;
(e) 0.1% by weight in homogeneous materials for polybrominated diphenyl ethers; and
(f) 0.01% by weight in homogeneous materials for cadmium.
This effectively restricts the levels of harmful chemicals that can occur within new electronic devices and of course, this means new mobile phones too. Non-compliance with this law can result in hefty fines. It must also be noted that batteries are not included within the RoHS's scope. There are separate battery laws in the UK (Batteries and Accumulators Regulations 2008) that cover agreed levels of cadmium and mercury within batteries. Again, this is based on another EU directive (2007/66/EEC).
One of the primary focuses of RoHS is to reduce environmental and biological damage to people in less developed countries where a lot of developed countries' waste electronics end up.
For further reading, you can read the legislation document here
For even further reading, there is of course an excellent Wikipedia article here