Business and Liquidity	9 Months Ended
Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business and Liquidity	1. BUSINESS AND LIQUIDITY Rallybio Corporation and subsidiaries (the "Company", "we", "our", or "us") is a clinical-stage biotechnology company built around a team of seasoned industry experts with a shared purpose and a track record of success in discovering, developing, manufacturing, and delivering therapies to meaningfully improve the lives of patients suffering from severe and rare diseases. In August 2021, the Company completed its initial public offering (“IPO”), pursuant to which it issued and sold 7,130,000 shares of the Company’s common stock, inclusive of 930,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $13.00 per share. The gross proceeds from the IPO, including the exercise of the underwriter's option to purchase additional shares were $92.7 million and the net proceeds were approximately $83.0 million, after deducting underwriting discounts and commissions and other offering costs. Prior to the IPO, the Company was a 100% owned subsidiary of Rallybio Holdings, LLC ("Rallybio Holdings"), a Delaware limited liability company which was incorporated in Delaware on March 22, 2018 and Rallybio Holdings held 100% of the outstanding membership units in five wholly-owned subsidiaries; Rallybio, LLC, Rallybio IPA, LLC, Rallybio IPB, LLC, Rallybio IPD, LLC, and IPC Research, LLC prior to the IPO and it's liquidation. On June 30, 2021, Rallybio Holdings completed a series of transactions pursuant to which (i) Rallybio IPD, LLC, a direct subsidiary of Rallybio Holdings that was formed in Delaware in May 2020, was converted from a Delaware limited liability company to a Delaware corporation and changed its name to Rallybio Corporation, and (ii) four direct subsidiaries of Rallybio Corporation, each a Delaware limited liability company (collectively the "Merger Subs"), each consummated a separate merger with one of Rallybio Holdings direct subsidiaries, other than Rallybio IPD, LLC (collectively the "Asset Subsidiaries"), with the Asset Subsidiaries surviving the mergers and Rallybio Holdings receiving common stock of the Company in exchange for its interest in each Asset Subsidiary, which resulted in the Asset Subsidiaries becoming subsidiaries of the Company and the Company becoming the only direct subsidiary of Rallybio Holdings. On July 28, 2021, immediately prior to the completion of the IPO, Rallybio Holdings liquidated and distributed 100% of the capital stock of the Company, consisting solely of common stock, to the unitholders of Rallybio Holdings. The liquidation of Rallybio Holdings and distribution of the capital stock of Rallybio Corporation to the unitholders of Rallybio Holdings is referred to as the “Liquidation” and these other transactions are collectively referred to as the “Reorganization.” As a result of the Reorganization and subsequent Liquidation, the unitholders of Rallybio Holdings became the holders of common stock of Rallybio Corporation, and the Company's condensed consolidated financial statements are subsequently reported from Rallybio Corporation. See Note 2 for the basis of presentation of these financial statements after the Reorganization and Liquidation discussed herein. The Company had cash and cash equivalents of $187.0 million at September 30, 2021. The Company currently expects that its cash and cash equivalents will be sufficient to fund its operating expenses and capital requirements for more than 12 months from the date the condensed consolidated financial statements are issued. However, we do not anticipate that the current cash and cash equivalents as of September 30, 2021 will be sufficient for us to fund any of our product candidates through regulatory approval, and we will need to raise substantial additional capital to complete the development and commercialization of our product candidates, if approved. We may satisfy our future cash needs through the sale of equity securities, debt financings, working capital lines of credit, corporate collaborations or license agreements, grant funding, interest income earned on invested cash balances or a combination of one or more of these sources. In March 2020, the World Health Organization characterized the novel coronavirus as a global pandemic. Although there is significant uncertainty as to the likely effects this disease may have in the future, to date there has not yet been a significant impact to the Company’s operations or financial statements.

Business and Liquidity

9 Months Ended

Sep. 30, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

1. BUSINESS AND LIQUIDITY

Rallybio Corporation and subsidiaries (the "Company", "we", "our", or "us") is a clinical-stage biotechnology company built around a team of seasoned industry experts with a shared purpose and a track record of success in discovering, developing, manufacturing, and delivering therapies to meaningfully improve the lives of patients suffering from severe and rare diseases.

In August 2021, the Company completed its initial public offering (“IPO”), pursuant to which it issued and sold 7,130,000 shares of the Company’s common stock, inclusive of 930,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $13.00 per share. The gross proceeds from the IPO, including the exercise of the underwriter's option to purchase additional shares were $92.7 million and the net proceeds were approximately $83.0 million, after deducting underwriting discounts and commissions and other offering costs.

Prior to the IPO, the Company was a 100% owned subsidiary of Rallybio Holdings, LLC ("Rallybio Holdings"), a Delaware limited liability company which was incorporated in Delaware on March 22, 2018 and Rallybio Holdings held 100% of the outstanding membership units in five wholly-owned subsidiaries; Rallybio, LLC, Rallybio IPA, LLC, Rallybio IPB, LLC, Rallybio IPD, LLC, and IPC Research, LLC prior to the IPO and it's liquidation. On June 30, 2021, Rallybio Holdings completed a series of transactions pursuant to which (i) Rallybio IPD, LLC, a direct subsidiary of Rallybio Holdings that was formed in Delaware in May 2020, was converted from a Delaware limited liability company to a Delaware corporation and changed its name to Rallybio Corporation, and (ii) four direct subsidiaries of Rallybio Corporation, each a Delaware limited liability company (collectively the "Merger Subs"), each consummated a separate merger with one of Rallybio Holdings direct subsidiaries, other than Rallybio IPD, LLC (collectively the "Asset Subsidiaries"), with the Asset Subsidiaries surviving the mergers and Rallybio Holdings receiving common stock of the Company in exchange for its interest in each Asset Subsidiary, which resulted in the Asset Subsidiaries becoming subsidiaries of the Company and the Company becoming the only direct subsidiary of Rallybio Holdings. On July 28, 2021, immediately prior to the completion of the IPO, Rallybio Holdings liquidated and distributed 100% of the capital stock of the Company, consisting solely of common stock, to the unitholders of Rallybio Holdings. The liquidation of Rallybio Holdings and distribution of the capital stock of Rallybio Corporation to the unitholders of Rallybio Holdings is referred to as the “Liquidation” and these other transactions are collectively referred to as the “Reorganization.” As a result of the Reorganization and subsequent Liquidation, the unitholders of Rallybio Holdings became the holders of common stock of Rallybio Corporation, and the Company's condensed consolidated financial statements are subsequently reported from Rallybio Corporation. See Note 2 for the basis of presentation of these financial statements after the Reorganization and Liquidation discussed herein.

The Company had cash and cash equivalents of $187.0 million at September 30, 2021. The Company currently expects that its cash and cash equivalents will be sufficient to fund its operating expenses and capital requirements for more than 12 months from the date the condensed consolidated financial statements are issued. However, we do not anticipate that the current cash and cash equivalents as of September 30, 2021 will be sufficient for us to fund any of our product candidates through regulatory approval, and we will need to raise substantial additional capital to complete the development and commercialization of our product candidates, if approved. We may satisfy our future cash needs through the sale of equity securities, debt financings, working capital lines of credit, corporate collaborations or license agreements, grant funding, interest income earned on invested cash balances or a combination of one or more of these sources.

In March 2020, the World Health Organization characterized the novel coronavirus as a global pandemic. Although there is significant uncertainty as to the likely effects this disease may have in the future, to date there has not yet been a significant impact to the Company’s operations or financial statements.