From what we read in the pages of the Bible regarding evil spirits, it is important to emphasize what the Word of God teaches in order to have a clear understanding of the subject of "spirits" - both as to their various names, but above all as to know how they behave and manifest themselves in their diabolic work in human life. We say in "human life" for the simple reason that "these spirits," according to the Bible, prefer to abide in humans rather than in beasts unless they are obliged to leave their preferred dwelling for a less desirable place (cf. the only case that the Bible gives, Matthew 8:28-34; Mark 5:1-17; Luke 8:26-39). Let it be clear from the start that our treatment of the subject refers only to "evil spirits" - demons as they are specifically called in the Bible and that has nothing to do with the human spirit. Obviously, before reviewing the various Bible passages concerning "spirits," we will give full etymological explanations of the Hebrew and Greek terms used in both the Old and New Testaments to understand better what the Bible teaches about this subject. The entire subject will be undertaken with the utmost Biblical coherency - with balanced exegesis and without forcing a meaning into the text that is not there. This, of course, is with the goal of gaining a clear and linear image of the subject. By this, we can completely understand how the forces of evil are manifested - their acts and operations in human life and at the same time, what must be done for those that are affected by these spirits for them to be liberated from these adversarial forces. We sincerely hope that this study can contribute to the enrichment and clarity of a topic that sometimes can create disagreement in the lives of believers and cause them to under estimate the many manifestations of these "spirits" that operate extensively in the lives of people who are faraway from God and His Word. Before rejecting the subject of "spirits" (especially considering that there is no unanimity on the subject amongst Christians), we suggest careful, critical and objective consideration. Past teachings based on popular traditions or beliefs, if not substantiated by the Word of God, will result in ongoing closed mindedness or cynicism. May the Spirit of the Lord illuminate our minds and hearts so that with all our life, zeal and above all, with all the love that we have for people that are in need of being helped and liberated, we can dedicate ourselves to their good, to the praise and glory of the greatest benefactor and liberator: Jesus Christ, the Son of the living God.