“blue sky”指蓝天法。是对各州通过的旨在调整、监督证券发行和交易、保护投资者免受欺诈的法令的通俗称谓。大多数蓝天法规定新发行证券要到州有关机关进行登记，以审核其发行文件的正确性和完整性。蓝天法也调整证券经纪人、销售人员的活动。投资百科中对其的定义如下：Blue sky laws are state-level, anti-fraud regulations that require issuers of securities to be registered and to disclose details of their offerings. Blue sky laws create liability for issuers, allowing legal authorities and investors to bring action against them for failing to live up to the laws' provisions.

“蓝天法”的名称来源于一名法官判决一起股票诈骗行为时称：“你们如此蒙蔽广大公众，如同把蓝天当作地产一样的出售。”

“蓝天法”归纳起来基本有以下四种类型：

一是防止欺诈类：以行政和法律手段来防止、制止股票交易中的欺诈违法行为；

二是公开型：将所有股票发行的有关资料及交易情况公诸于众，争取最大的公平与公正；

三是管理型：强调交易的管理，以便维护股市的正常秩序，维护公众的利益；

四是登记型：为尽量杜绝交易中的不正当行为，凡股票经纪人，须经严格的资格审查，履行登记手续，才能上市。

以下为某股东协议中的蓝天法条款：

Blue Sky. Use its best efforts to register and qualify the securities covered by such registration statement under such other securities or Blue Sky laws of such jurisdictions as shall be reasonable requested by the Holders, provided that the Company shall not be required in connection therewith or as a condition thereto to qualify to do business or to file a general consent to service of process in any such states or jurisdictions unless the Company is already subject to service in such jurisdiction and except as may be required by the Securities Act.

蓝天。尽最大努力根据持有人合理要求的司法管辖区的其他证券法律或蓝天法律，对该登记所涉及的证券进行登记并使其合格，但前提是公司无需在该州或司法管辖区内以此作为其具有开展业务或提交送达法律程序文件的一般同意的资格的条件，除非公司已需受限于该司法管辖区的送达，且《证券法》可能规定的情况除外。