Executive buy-in is crucial for the success of any initiative within the organization. It is the alignment and the agreement from the top-down and bottom-up. Security initiatives can originate from any level within the organization but should normally start at the managerial level. Getting executives to support the Security initiative will ultimately determine the success and longevity of the program.
Depending on the nature of the initiative, the result of executive support can be a verbal confirmation, or a memo to staff members showing support coupled with capital funding for the initiative. In relation to initiating Defensible Security (DefSec) within your organization, a verbal confirmation alone might not be sufficient; there should be tangible outcome of executive support (e.g. a meeting with executives followed by an email to relevant stakeholders/Directors expressing support).
At a hygiene level, executive support is achieved by presenting to executives, expressing the importance of DefSec. Beyond compliance level, executive support will include capital funding.