This study examines the monitoring effects of institutions, outside directors, and outside blockholders by seeing managers` selection of antitakeover measures. In this paper, we hypothesize that managers use antitakeover techniques to entrench themselves when they are not monitored closely. Consequently, we hypothesize that institutional ownership, outside membership on board of directors, outside directors ownership, and outside blockholder ownership are less in firms which adopt harmful antitakeover measures.  This paper analyzes whether the degree of monitoring by institutions, outside directors, and outsides blockholders influences managers` adoption of different types of takeover defenses. We find interesting empirical results. First, aggregate institutional ownership is positively correlated with the likelihood of antitakeover techniques adoption. This result implies that institutional investors are passive. Second, total and active blockholder ownership is higher at firms that do not propose any defensive tactics. passive blockholder ownership is highest at fair price firms but low at poison pills firms. Ownership concentration by outside investors increases monitoring and reduces agency problems. Thirid, outside board monitoring is ineffective.