Sahel Ahyaie Assar

How Sahel Helps Clients

Sahel’s experience sits at the intersection of U.S. tax law, wealth management and the evolving digital asset landscape, with over two decades of experience guiding ultra-high-net worth individuals, multinational institutions and financial institutions through complex international tax and regulatory environments. Sahel leads the Blockchain and Digital Asset Practice Group where her work spans the legal, regulatory, and policy dimensions of emerging financial infrastructure, tokenization and DeFi. Sahel also represents clients before the Internal Revenue Service and state governmental tax authorities (i.e., the California Franchise Tax Board) as well as in the U.S. Tax Court.

Sahel has extensive experience advising ultra-high-net-worth individuals and their closely held business interests and real property holdings with respect to international cross-border tax planning (inbound and outbound), international trusts and estates for families of substantial wealth, and compliance with U.S. tax reporting requirements.

Foreign financial institutions, fiduciaries and family offices find her years as a practitioner in Zurich, Switzerland to be particularly helpful when it comes to providing them with advice related to U.S. tax reporting, regulatory, banking and international cross-border matters. Her practice also focuses on tax planning, structuring and related business advice for a wide range of corporations, LLCs, partnerships, trusts and individuals in both domestic and international tax matters. Sahel advises foreign individuals with respect to investments in the United States, pre-immigration planning, expatriation, the application of tax treaties, U.S. withholding obligations, offshore tax compliance, residency issues triggering U.S. taxation, and income, transfer tax and reporting obligations of foreigners.

In addition to providing advice to clients with respect to her area of expertise, Sahel often acts as a trusted advisor to a number of wealthy families and as an ambassador to financial institutions, family offices and ultra-high net worth individuals by finding the best resources at Buchanan to assist them with their overall legal needs.

Prior to joining Buchanan, Sahel held senior legal and advisory roles across global financial centers. As a private banker and trusts and estates strategist at Credit Suisse in Zurich and managing attorney of her own firm, she led cross-jurisdiction legal teams in high-stakes trust recovery cases across Europe, the Middle East, and Asia.

Earlier positions with AM Law Top 50 law firms as well as at KPMG’s Washington National Tax Mergers & Acquisition Group contributed to her technical U.S. tax foundation.

Sahel is the Leader of Buchanan's Blockchain and Digital Asset Practice Group where she develops, monitors, and assesses the legal needs of clients with respect to all things blockchain, crypto, and digital assets and is recognized as a thought leader on matters pertaining to taxation of cryptocurrencies. She is frequently quoted by major outlets, including the Wall Street Journal, Bloomberg, Business Insider, Law360, Daily Tax Report, where her analysis has helped shape public understanding of IRS enforcement trends, OECD regulatory frameworks, and the fiscal policy landscape affecting digital assets. Additionally, Sahel is a sought-after speaker and moderator for outlets covering digital assets and tax law, hosted by the American Bar Association, International Fiscal Association, Wharton School, Brookings, and others.

Sahel holds two LL.M. degrees from the Georgetown Law Center and has been recognized in The Best Lawyers in America (2023-2025) for tax law. Fluent in French, Farsi, English, and semi-fluent in German and Spanish, with a global perspective rooted in deep professional and cultural fluency, Sahel is a reliable technician on matters pertaining to U.S. federal income tax and a voice in the dialogue shaping digital finance. Sahel has strong affiliations with Switzerland and was named a 2021 Greater Zurich Honorary Ambassador.

What Clients Can Expect

Clients can expect to find Sahel professional, thorough and dedicated, with a high drive for excellence. The most important aspect of her success is her relentless presence and availability to each of her clients.

I have found that the reason I am hired is because clients trust my knowledge, judgment and the fact that I will be a zealous advocate for them. In addition, my expertise in U.S. federal taxes, fluency in additional languages and experience overseas in Europe and the Middle East provides a unique platform to connect with international families.

Outside the Office

Sahel enjoys sports, including tennis, skiing, horseback riding, as well as reading, the arts and culinary endeavors. Had she not become a lawyer, she would have pursued a career as a writer.

Proof Points

• Provide advice to U.S. and foreign individuals and companies with respect to inbound and outbound U.S. federal income taxation.
• Provide advice regarding U.S. tax compliance involving international information returns.
• Assist with taxation and matters pertaining to digital assets, including cryptocurrency.
• Represent foreign financial institutions, family offices and private individuals with all aspects of international tax compliance enforcement requirements including international tax reporting, specifically.
• Provide assistance with international tax and wealth planning for ultra-high net worth individuals and families including pre-immigration and foreign trusts and estates planning advice.
• Assist foreign lawyers with cross-border matters pertaining to international tax including competent authority and transfer pricing.
• Represent clients with matters before the Internal Revenue Service and the California Franchise Tax Board.
• Served as an independent technical expert on issues involving U.S. federal income tax laws before the Commercial Division of the Eastern Caribbean Supreme Court in the BVI.
• Successfully represented numerous individuals involving unreported foreign income and foreign assets under IRS Offshore Voluntary Disclosure Programs, Streamlined Foreign Offshore Procedures and Streamlined Domestic Offshore Procedures, Delinquent International Information Return Submission Procedures, Delinquent Report of Foreign Bank and Financial Account (FBAR) Submission Procedures and IRS Service Center filings
• Successfully argued for significant penalty abatements for clients before the Department of Treasury’s IRS and the California Franchise Tax Board, respectively.