Costar's three largest insider shareholders as of September 12, 2026 are Andrew C Florance (Founder And Ceo, 1.81Mn shares), Frank Simuro (Chief Technology Officer, 414.49K shares), Frank Simuro (Chief Technology Officer, 414.49K shares).
| # | Insider | Position | Direct | Indirect | Total | Share of Insiders | Last Filed |
|---|---|---|---|---|---|---|---|
| 1 | Andrew C Florance | Founder And Ceo | 1,806,165 | 0 | 1,806,165 | 51.0% | 05 Aug, 2026 |
| 2 | Frank Simuro | Chief Technology Officer | 414,491 | 0 | 414,491 | 11.7% | 17 Mar, 2026 |
| 3 | Scott T Wheeler | Chief Financial Officer | 303,417 | 0 | 303,417 | 8.6% | 30 Apr, 2024 |
| 4 | Frederick G. Saint | President, Marketplaces | 278,415 | 0 | 278,415 | 7.9% | 04 Aug, 2026 |
| 5 | Christopher J Nassetta | Director | 229,715 | 0 | 229,715 | 6.5% | 02 Dec, 2024 |
| 6 | Lisa Ruggles | Senior Vp, Global Operations | 174,915 | 0 | 174,915 | 4.9% | 17 Mar, 2026 |
| 7 | Gene Boxer | General Counsel And Secretary | 95,463 | 0 | 95,463 | 2.7% | 17 Mar, 2026 |
| 8 | Michael J Desmarais | Chief Human Resources Officer | 87,725 | 0 | 87,725 | 2.5% | 17 Mar, 2026 |
| 9 | Louise S Sams | Director | 28,671 | 0 | 28,671 | 0.8% | 24 Jun, 2026 |
| 10 | Robert W Musslewhite | Director | 26,539 | 0 | 26,539 | 0.7% | 24 Jun, 2026 |
| 11 | John W Hill | Director | 22,993 | 0 | 22,993 | 0.6% | 10 Aug, 2026 |
| 12 | Cynthia Cammett Cann | Chief Accounting Officer | 18,822 | 0 | 18,822 | 0.5% | 10 Aug, 2026 |
| 13 | Laura Cox Kaplan | Director | 17,835 | 0 | 17,835 | 0.5% | 05 Aug, 2024 |
| 14 | Rachel C Glaser | Director | 12,419 | 0 | 12,419 | 0.4% | 24 Jun, 2026 |
| 15 | John L Berisford | Director | 11,235 | 0 | 11,235 | 0.3% | 24 Jun, 2026 |
| 16 | Angelique G. Brunner | Director | 10,166 | 0 | 10,166 | 0.3% | 11 Sep, 2025 |
Each row is that insider’s most recently reported position, from Form 4 filings over the last 60 months — which is why this total does not tie to the quarterly series above, where a quarter counts only the insiders who filed in it. Shares held through a fund or institutional portfolio are counted on the institutional ownership page instead.
| Date | Insider | Position | Transaction | Shares | Price | Value | Shares Held After | Ownership |
|---|---|---|---|---|---|---|---|---|
| 05 Aug, 2026 | John W Hill | Director | Disposed S | 3,500 | $30.21 | $105.74K | 22,993 | Direct |
| 07 Aug, 2026 | Cynthia Cammett Cann | Chief Accounting Officer | Disposed S | 4,788 | $30.78 | $147.37K | 18,822 | Direct |
| 04 Aug, 2026 | Andrew C Florance | Founder And Ceo | Acquired P | 83,300 | $29.89 | $2.49Mn | 1,806,165 | Direct |
| 01 Aug, 2026 | Frederick G. Saint | President, Marketplaces | Disposed F | 1,436 | $28.76 | $41.30K | 278,415 | Direct |
| 01 Aug, 2026 | Cynthia Cammett Cann | Chief Accounting Officer | Disposed F | 1,077 | $28.76 | $30.97K | 23,610 | Direct |
| 31 Jul, 2026 | Robin Jack Rossmann | Chief Financial Officer | Acquired A | 34,771 | $0.00 | $0 | 34,771 | Direct |
| 31 Jul, 2026 | Cynthia Cammett Cann | Chief Accounting Officer | Acquired A | 26,078 | $0.00 | $0 | 26,078 | Direct |
| 23 Jun, 2026 | Rachel C Glaser | Director | Acquired A | 8,262 | $0.00 | $0 | 12,419 | Direct |
| 23 Jun, 2026 | Louise S Sams | Director | Acquired A | 8,262 | $0.00 | $0 | 28,671 | Direct |
| 23 Jun, 2026 | John L Berisford | Director | Acquired A | 8,262 | $0.00 | $0 | 11,235 | Direct |
| 23 Jun, 2026 | Robert W Musslewhite | Director | Acquired A | 8,262 | $0.00 | $0 | 26,539 | Direct |
| 23 Jun, 2026 | John W Hill | Director | Acquired A | 8,262 | $0.00 | $0 | 26,493 | Direct |
| 23 Jun, 2026 | Angelique G. Brunner | Director | Acquired A | 8,262 | $0.00 | $0 | 18,428 | Direct |
| 15 Jun, 2026 | Cynthia Cammett Cann | Chief Accounting Officer | Disposed F | 461 | $32.04 | $14.77K | 24,687 | Direct |
| 01 May, 2026 | Andrew C Florance | President And Ceo | Acquired P | 68,330 | $35.17 | $2.40Mn | 1,719,765 | Direct |
| 01 May, 2026 | Andrew C Florance | President And Ceo | Acquired P | 3,100 | $35.82 | $111.04K | 1,722,865 | Direct |
| 15 Mar, 2026 | Michael J Desmarais | Chief Human Resources Officer | Disposed F | 2,873 | $43.63 | $125.35K | 87,725 | Direct |
| 15 Mar, 2026 | Lisa Ruggles | Senior Vp, Global Operations | Disposed F | 2,977 | $43.63 | $129.89K | 174,915 | Direct |
| 15 Mar, 2026 | Michael J Desmarais | Chief Human Resources Officer | Disposed F | 2,873 | $43.63 | $125.35K | 87,725 | Direct |
| 15 Mar, 2026 | Lisa Ruggles | Senior Vp, Global Operations | Disposed F | 2,977 | $43.63 | $129.89K | 174,915 | Direct |