Mark is Chairman Emeritus of the firm and concentrates his practice in New York State and New York City tax matters. He has more than 40 years of experience with federal, multistate, state and local taxation -- and may be best known for his public speaking on tax topics. Mark splits his time between the Firm's New York City and Buffalo offices.

Mark has represented numerous Fortune 500 companies in connection with corporate, withholding and sales tax audits as well as dozens of individuals who appear on the Forbes 400 list of wealthiest individuals in the United States. He has also been quoted in dozens of newspapers and periodicals, including The New York Times, The Wall Street Journal, Newsday, The Boston Globe and the Associated Press. Mark has appeared as a state tax expert on CNBC, CNN and other news outlets.

Mark taught courses in the Tax Certificate Program in the School of Management at the University of Buffalo on state taxation and tax practice and procedure. He is a member of The CPA Journal editorial review board and has written numerous books, articles and treatises on the subject of multistate taxation. Mark is the co-author of the ABA Sales & Use Tax Desk Book, CCH's New York Residency and Allocation Audit Handbook; New York Sales and Use Tax Answer Book, the New York State Bar Association's Contesting New York State Tax Assessments, 4th Edition; and CCH's New York Sales and Use Tax. Mark is also a contributor to numerous professional and industry-focused publications. 


State University College at Buffalo, B.S., summa cum laude

University at Buffalo School of Law, J.D., magna cum laude


  • New York
  • New Jersey
  • Florida
  • U.S. Supreme Court


  • Listed, Best Lawyers in America (Tax Law, Litigation and Controversy -Tax) 1995 - 2024
  • Listed, New York Metro Super Lawyers (Tax) 2019 - 2023 
  • Listed, Upstate New York Super Lawyers (Tax) 2007 - 2023
  • Listed, Best Lawyers in America "Lawyer of the Year" (Litigation and Controversy - Tax), 2021
  • Listed, Buffalo Business First/Buffalo Law Journal’s Legal Elite of Western New York Legal Leader, 2018 - 2020

  • Martindale-Hubbell, 1998-2022 – highest possible peer review rating in legal ability & ethical standards for 24 years

  • Who's Who in American Law

News & Insights

Multimedia & Podcasts

  • Stupid Sales Tax Rules

    Have you ever really looked into some of the distinctions between what makes an item taxable or nontaxable in New York? Well, we have, and some of the rules are just plain outrageous. Joe is joined by Mark Klein, Joe Endres, and Josh Lawrence to discuss some of New York State’s silliest sales tax rules. You’ll be shocked at how the tiniest difference can result in a hefty sales tax bill. The panel shares stories about some of the niche sales tax issues that have come up on audit.

  • A Brief History of State and Local Tax Part 2

    In Episode Two of “State Tax Talks with Joe Tantillo,” Joe and the "Tax Titans", Paul Comeau and Mark Klein, continue their discussion of the development of SALT legal practice.

  • A Brief History of State and Local Tax

    In Episode One of “State Tax Talks with Joe Tantillo,” Joe provides an overview of the development of SALT legal practice, as told by experts, Paul Comeau and Mark Klein (or as we call them, the “Tax Titans”).

    You won’t want to miss this!

Jump to Page

Necessary Cookies

Necessary cookies enable core functionality such as security, network management, and accessibility. You may disable these by changing your browser settings, but this may affect how the website functions.

Analytical Cookies

Analytical cookies help us improve our website by collecting and reporting information on its usage. We access and process information from these cookies at an aggregate level.

Mark S. Klein / News & Insights