Forms to file with SEC:

Form Used For Filed By Key Contents Trigger/Event
S-1 IPO (Initial Public Offering) Private company going public Prospectus, financials, risk factors First-time public offering
S-3 Follow-on offering (seasoned issuers) Public companies Shelf registration, streamlined disclosure Secondary or follow-on offerings
S-4 M&A deals with stock/debt issuance Acquirer (and target if public) Proxy, prospectus, deal terms, pro formas Stock-financed mergers or exchange offers
S-8 Employee stock/benefit plans Public companies Securities for compensation plans Stock/options granted to employees
F-1/F-3/F-4 Foreign issuer versions of S-1/S-3/S-4 Foreign private issuers Same as above, but tailored to foreign filers IPOs, follow-ons, M&A for non-U.S. firms

Reg M-A by SEC:

Reg M-A = Regulation Mergers & Acquisitions. It’s an SEC regulation that governs disclosures made in business combinations, such as:

Form Used For Who Files It Reg M-A Applies? Notes
S-4 Registering securities in stock-based M&A Acquirer ✅ Yes Includes proxy, prospectus, pro forma financials
Schedule TO Making a tender or exchange offer Acquirer ✅ Yes Discloses terms of offer
Schedule 14D-9 Responding to a tender offer Target company ✅ Yes Target’s formal position on the offer
Schedule 13E-3 Going-private transactions Company or affiliates taking it private ✅ Yes Protects minority shareholders
DEFM14A Merger proxy for shareholder vote Target or acquirer ✅ Yes Used when shareholder approval is needed

WKSI (Well Known Seasoned Issuer) vs Seasoned Issuer vs Unseasoned Issuer:

Feature WKSI Seasoned Issuer Unseasoned Issuer
SEC Filing History ≥ 12 months ≥ 12 months < 12 months OR not timely
Public Float ≥ $700 million OR ≥ $1B in debt ≥ $75 million < $75 million
Form Eligibility S-3 with automatic shelf S-3 (but not automatic) S-1 (long-form only)
Shelf Registration Effective? Immediately (automatic shelf) Only after SEC review and declaration Not allowed (must file S-1)
Shelf Validity Period 3 years 3 years Not applicable
Pay-as-you-go Filing Fees ✅ Yes ❌ No ❌ No
Use of Free Writing Prospectus ✅ Yes (before & after filing) ✅ Yes (after filing only) ❌ No
Marketing Flexibility Maximum Moderate Minimal
Typical Example Apple, Microsoft, JPMorgan Mid-cap public companies Recent IPOs, early-stage filers