RoHS is an initialism for Restriction on the use of certain Hazardous Substances. RoHS was first introduced as a European Union directive (2002/95/EC), which went in force in 2003. It requires heavy metals including lead, mercury, cadmium, and hexavalent chromium and flame retardants, such as polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE), to be substituted by safer alternatives.

In 2011, a New RoHS directive (2011/65/EU) came in force. This new directive is referred to as RoHS 2. RoHS extended the scope of the requirements to all electrical and electronic equipment (EEE) and cables and spare parts (to be phased in through July 2019). It also provided coherence with other EU legislation, such as CE marking and declaration of conformity and REACH (a general act regulating registration, evaluation, authorization and restriction of chemical substances). As a CE marking Directive, RoHS 2 requires the manufacturer, prior to placing a product on the European market, to produce the required technical documentation to describe the internal product control procedures put in place by the manufacturer to ensure there are no restricted substances in EEE.

The Maximum Concentration Value (MCV) for heavy metals and flame retardants covered by RoHS are as follows:

Lead (0.1 %)
Mercury (0.1 %)
Cadmium (0.01 %)
Hexavalent chromium (0.1 %)
Polybrominated biphenyls (PBB) (0.1 %)
Polybrominated diphenyl ethers (PBDE) (0.1 %)
For more detailed information, see European Commission’s RoHS 2 FAQ

I don’t sell in Europe; does RoHS apply to my EEE product?

If you sell components to manufacturers that do sell products containing your components in Europe, you may still have to comply. If your products or components will not be sold in Europe, the European Directive does not directly apply; however, several states have enacted legislation which you need to be aware of in case the product is sold in those states. The state directives as of late 2017 consist of the following:

California RoHS law requires ‘covered electronic devices’ sold in the state to meet the same requirements as those found in European Union’s RoHS legislation. The regulations prohibit a covered electronic device from being sold or offered for sale in California if that device is prohibited from being sold or offered for sale in the EU due to the presence of lead, mercury, cadmium, or hexavalent chromium (does not include PBB or BBDE) above certain maximum concentration values (MCVs).

The MCVS are as follows:

lead, mercury, and hexavalent chromium — 0.1% by weight.
cadmium — 0.01% by weight.
Note that polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE) are not covered by the California law. California Law does not require manufacturers of covered electronic devices to register with California. However, manufacturers must submit an annual report to the California Integrated Waste Management Board (CIWMB) that includes information regarding the use of restricted substances in covered electronic devices.

Read more about RoHS law requirements here