It's an operating agreement. The issue is what the operating agreement entails. A very complete agreement would include things like buy-sell, dispute resolution, employment terms for members-employees, so on. A very complete agreement can run 50 pages or more.
You can't just grab a shareholder agreement and try to fit that to an LLC as the form, legal and tax issues can be considerably different. The best advice is simple, namely hire an attorney who has expertise in LLC agreements.
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I agree with Attorney Murillo that an Operating Agreement would normally serve this function. It is best to have this form prepared by an attorney so that it can be customized for your LLC. There are many issues that need to be addressed.
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Apples and Oranges. The Operating Agreement for an LLC spells out the terms of the relationship between the members and dictates the terms of management of the LLC. Shareholder agreements spell out the relationship between the shareholders and the corporation. You should talk to an attorney about drafting an operating agreement for an LLC rather than doing a copy and paste job. Badly written operating agreements are fertile grounds for protracted litigation.