The following is the Jan. 17, 201b Congressional Research Service report, Iran Sanctions.

From the Report:

US Naval Institute News, February 1, 2018 – The multilateral nuclear accord (Joint Comprehensive Plan of Action, or JCPOA) provides Iran broad relief from U.S., U.N., and multilateral sanctions on Iran’s civilian economic sectors, including U.S. secondary sanctions (sanctions on foreign firms that do business with Iran). On January 16, 2016, upon the International Atomic Energy Agency (IAEA) certification that Iran had complied with the stipulated nuclear dismantlement commitments, U.S. Administration
waivers of relevant sanctions laws took effect, relevant executive orders (E.O.s) were revoked, and corresponding U.N. and EU sanctions were lifted.
Under U.N. Security Council Resolution 2231, nonbinding U.N. restrictions on Iran’s development of nuclear-capable ballistic missiles and a binding ban on its importation or exportation of arms remain in place for several years. Iran was able to develop its nuclear and missile programs and to assist pro-Iranian regional groups and governments even when strict sanctions were in place. Also remaining in place, is a general ban on U.S. trade with and investment in Iran, including regulations barring transactions between U.S. and Iranian banks, and U.S. sanctions imposed because of Iran’s support for terrorism, its human rights abuses, its interference in specified countries in the region, and its missile and advanced conventional weapons programs, as well as sanctions on the Islamic Revolutionary Guard Corps (IRGC), and designated commanders, subunits, and affiliates. Some additional sanctions on these entities and activities were made mandatory by the Countering America’s Adversaries Through Sanctions Act (P.L. 115-44), which also increases sanctions on Russia and North Korea.
As part of a shift to assertively counter Iran’s regional activities and strategic weapons programs, the Trump Administration has threatened to cease implementing the JCPOA unless Congress and U.S. allies successfully address the agreement’s weaknesses. Thus far, including on January 12, 2018, the administration has continued to implement the agreement by exercising waivers of
sanctions laws suspended in accordance with the JCPOA, while continuing to impose sanctions on missile- and IRGC-related entities and on Iranian human rights violators. However, the President said on January 12, 2018, that he would not renew any more waivers, the next one being due on May 12, unless his conditions for fixing the JCPOA are met. Because the President has also not certified Iranian compliance with the JCPOA under the Iran Nuclear Agreement Review Act (P.L. 114-17), Congress might act to reimpose Iran sanctions.
The reimposition of U.S. secondary sanctions would undoubtedly harm Iran’s economy. Iran’s economy shrank by 9% in the two years that ended in March 2014, before stabilizing since 2015 as a result of modest sanctions relief under an interim nuclear agreement. Sanctions caused Iran’s crude oil exports to fall from about 2.5 million barrels per day (mbd) in 2011 to about 1.1 mbd by mid-2013, and made inaccessible more than $120 billion in Iranian reserves held in banks abroad.
Sanctions relief has enabled Iran’s oil exports to return to nearly pre-sanctions levels, allowed Iran to regain access to funds held abroad and reintegrate into the international financial system, and helped Iran achieve about 7% overall economic growth in 2016, with similar growth in 2017.
Foreign energy firms have begun making new investments in Iran’s energy sector and major aircraft manufacturers have sold Iran’s commercial airlines new passenger aircraft. The relief from sanctions on Iran’s most vital sectors helped Iran’s President Hassan Rouhani politically, contributing to his victory in the May 19, 2017, presidential election, but did not satisfy significant economic grievances in Iran that sparked widespread unrest in December 2017- January 2018.