GNU Lesser General Public License v2.1

WeakUsed by: GNU C Library, Qt (historical usage)

Description

A weaker copyleft license that allows linking with proprietary software while still requiring modifications to the licensed code to remain open-source.

Key Features

Weak copyleft
Library-specific provisions
No patent clauses
Combination rights

History & Context

Created in 1991 as Library GPL, renamed in 1999. Designed for shared libraries.

Compatibility
What is license compatibility?
License compatibility indicates whether code under this license can be combined with code under other licenses in the same project without legal conflicts.

License	Compatibility
With gpl	GPL-3.0 can incorporate LGPL-2.1 code
With mit	LGPL-2.1 can incorporate MIT-licensed code
With bsd	LGPL-2.1 can incorporate BSD-licensed code
With proprietary	Yes (for linking)

License Details

Copyleft Strength

Weak

Legal Enforceability

Proven in court cases

Notable Projects

GNU C LibraryQt (historical usage)

License Provisions

AttributionRequired

Source codeModified files only

Modification clauseMust share changes to library

WarrantyDisclaimer included

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