The book "Co-parenting and the best interests of the child" deals with the reforms introduced in Family Law by Law 4800/2021, specifically the significant changes in the upbringing and care of minor children. This is a modern legal framework, imposed by international conventions and the ECHR, which is governed by: the legal system of joint exercise of parental responsibility, the principle of equality of parents in their responsibilities and rights towards the child, the obligation of the parent residing with the child to strengthen their relationship with the other parent and their relatives, the autonomy of private will, the promotion of mediation, and the subsidiary role of the court. The subject of the monograph is not only the presentation and analysis of the provisions of family law established by Law 4800/2021, but mainly their correct practical application with the best interests of the child in mind. In this context, the following are presented: issues of parental responsibility and joint decision-making, the residence of the child and alternating residence, the right to communication and parental alienation syndrome, domestic violence, temporary regulation of family relationships, family mediation and the opinion of the child, good practices through case law examples in foreign countries that apply the legal regime of joint exercise of parental responsibility. The work is addressed especially to lawyers and judges, law students, but also to anyone else (mental health professionals, educators, mediators) who wishes to be informed about the new provisions of family law concerning parent-child relationships.