Vertical organizational structure means a strict top down or bottom up structure. Typically, a rigid top down vertical organizational structure has been a favored form for many business and other type organizations. In such an organization, the chain of command is usually very important and breaking it is considered very wrong. In faster moving, dynamic conditions, a vertical organizational structure can become very inefficient, for example, requiring decisions to slowly go through many people along the vertical chain of command before actions can be made by those who need permission to act. Horizontal organizational structure means a flat or closer to flat organizational structure. In a perfectly horizontal structure, there are no leaders, so usually this means a structure that is still vertical, but has been made more horizontal than what is typically referred to as vertical. Where the line is drawn is not exactly clear to me and perhaps depends upon all factors in a particular example and conversation. In general, any large organizational structure has both vertical and horizontal aspects to it and depending on whether it is considered to be more vertical or more horizontal results in what it is called. Vertical organizational structures also tend to create boundaries between departments or branches in a larger organization, because for a person down one branch must go up the chain of command on his branch and then down the chain of command on the other branch in order to interact with someone down the chain of command on a different branch. Having to do this tends to make such inter group interaction so hard as to strongly discourage it. Just think "bloated bureaucratic obstacle course from hell". To have a more horizontal organizational structure means cutting out levels of mid-management which results in allowing more horizontal level of authority. It does grant more authority to various horizontal layers of employees. This can help improve communication, remove inefficient bureaucratic steps, reduce unnecessary work and speed up the whole process. The problem with this can be whether or not the employees given this extra responsibility are in fact capable of handling it. This becomes the trade off between the two organizational forms and why some organizations vacillate between being more vertical and more horizontal are different times. Finding a good mix greatly depends upon the people actually making up the structure, so when the people change, how well the structure is working can change too, thus requiring a change towards being more or less vertical or horizontal. There is another structural form called the circular organizational structure. I'm not an expert in this field, so I'm only giving my best understanding of this question. I find elements of horizontal and circular organizational structures to be so close as to not really understand the difference. However, being an engineer who has worked on a team in an organization that tended to be fairly horizontal, I think of circular having a particular meaning. To me, it means a process of having the leader provide overall direction, defining the goal, and then creating a cycle of work and exchange of information that repeatedly goes through the group, back up to the leader, so that everyone involved inputs ideas and keeps good strong communications open through all involved. By this, I mean that the leader is open to hearing and understanding what those under him are saying and keeps actively abreast with what they are doing. Similarly, as various members of the team are working on things, they keep others abreast of what they are doing, so that people stay on the same page. But, isn't this just part of being a fairly horizontal organization? Well, English is not one of my better skills, so I'll leave my attempt to answer this question as it is. Maybe an expert in organizational structures will come along and give a better answer.