The Function of Fiat-Backed Stablecoins
Both USDT (Tether) and USDC (Circle) are designed to flawlessly maintain a 1:1 price peg with the US Dollar. They achieve this by holding physical fiat reserves, treasury bills, and commercial paper off-chain.
For every digital USDT or USDC token minted on the blockchain, the issuing company theoretically holds exactly $1 in a bank vault to back it. The controversy lies entirely in proving those reserves exist.
Tether (USDT): The Indispensable Giant
Tether is the oldest and largest stablecoin. It possesses the deepest liquidity across all exchanges globally, particularly in Asia and emerging markets. If you want maximum trading volume and pair availability, USDT is king.
However, Tether's history is notoriously opaque. They have faced heavy legal scrutiny for refusing full, independent audits, preferring "attestations." While they claim to be fully backed by US Treasuries, critics have long feared systemic risk due to their offshore banking structure.
USD Coin (USDC): The Regulatory Darling
USDC is minted by Circle, an entity heavily integrated into the US regulatory framework. It prioritizes extreme transparency, publishing monthly attestations from top accounting firms.
USDC holds its reserves exclusively in cash and short-duration US Treasuries housed in major regulated American banks. For institutions and risk-averse investors holding massive sums of capital on-chain, USDC is vastly preferred over USDT due to its compliance record.
Censorship Risk and Freezing
Because both tokens are centralized, the issuing companies (Tether and Circle) possess the master keys to the smart contracts. They can—and frequently do—"blacklist" and freeze specific wallet addresses at the request of law enforcement.
If you hold USDC or USDT on a hardware wallet, you have custody against hackers, but you do not have custody against state censorship. For true censorship resistance, you would need algorithmic stablecoins (like DAI), though they carry their own severe collateral risks.