- Athens Stock Exchange (ASE)
- Auction Market Preferred Stock (AMPS)
- Auction markets
- Auction rate preferred stock (ARPS)
- Audit
- Audit trail
- Auditor's certificate
- Auditor's report
- Aunt Millie
- Australian Stock Exchange (ASX)
- Autarky
- Autex
- Authentication
- Authority bond
- Authorized shares
- Autocorrelation
- Automated bond system (ABS)
- Automated Clearing House (ACH)
- Automated Customer Account Transfer (ACAT)
- Automated Export System
- Automated Order System (AOS)
- Automated Pit Trading (APT)
- Automated teller machine (ATM)
- Automatic Data Processing (ADP)
- Automatic exercise
- Automatic extension
- Automatic funds transfer
- Automatic investment program
- Automatic reinvestment
- Automatic stay
- Automatic transfer service (ATS) account
- Automatic withdrawal
- Autoquote
- Autoregressive
- Auto-Regressive (AR) Process
- Autoregressive Conditional Heteroskedasticity (ARCH)
- Availability
- Availability float
- Available cash flow
- Available on the way in