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William Long
Partner at Sidley Austin LLP, UK


WILLIAM LONG is a global co-leader of Sidley's highly ranked Privacy and Cybersecurity practice and also leads the EU data protection practice at Sidley. William advises international clients on a wide variety of GDPR, data protection, privacy, information security, social media, e-commerce and other regulatory matters.  

William has been a member of the European Advisory Board of the International Association of Privacy Professionals (IAPP) and on the DataGuidance panel of data protection lawyers. He is also on the editorial board of e-Health Law & Policy and also assists with dplegal (“data privacy” legal), a networking group of in-house lawyers in life sciences companies examining international data protection issues.

Representative matters have included: 

  • Advising numerous international companies on the GDPR.
  • Advising companies on data privacy issues with Big Data, Internet of Things and profiling. 
  • Advising a global e-commerce company on dealing with an international data security breach.
  • Assisting a global manufacturing company with a global data protection project including implementation of Binding Corporate Rules.

William was previously in-house counsel to one of the world’s largest international financial services groups. He has been a member of a number of working groups in London and Europe looking at the EU regulation of e-commerce and data protection and spent a year at the UK’s Financial Law Panel (established by the Bank of England), as assistant to the Chief Executive working on regulatory issues with online financial services.

William is recognized in Chambers UK 2019 for Data Protection and Information Law, with sources telling the publication he brings “a broad depth of knowledge on the key areas of law,” whilst in the 2017 edition, clients cite him as “very knowledgeable, very practical and always solution-driven.” He is recognized in the LMG Life Sciences Guide 2014 for Intellectual Property and Who’s Who Legal 2017 for TMT. He has also been listed in Best Lawyers 2019 for Privacy & Data Protection Law and Who's Who Legal: Data 2019. William is recognized for both Data Protection, Privacy & Cybersecurity and Pharmaceuticals & Biotechnology in The Legal 500 UK 2017, with clients noting that his “‘forward-thinking and proactive approach keeps him ahead of the curve’” and describing his advice as “‘thorough, timely and on the leading edge.’” He is also included in the 2018 edition of Best Lawyers for Privacy & Data Protection and is listed for Data Security in Who’s Who Legal: UK Global Elite Thought Leaders 2019.

William is also the author of a new book on the EU General Data Protection Regulation and a contributor to a number of books on data protection, including leading legal text books published by BNA in the area of privacy, cloud computing and the use of health data. William has been interviewed widely for his thought leadership, including in such leading publications as the international New York Times, Financial Times, Guardian and writes for a number of publications including Data Protection Law & Policy, Computer Weekly, Cloud Pro and CIO Today.

Agenda Sessions

  • On-going Tensions Surrounding GDPR and Data Sharing for the Pharmaceutical Industry

  • PANEL DISCUSSION Legal Challenges for Managing Clinical Research Data