The guiding principle in custody and visitation disputes is what is in the best interest of the child(ren).  Custody refers to legal custody as well as physical custody.  The person that makes the religious, educational and medical decisions for the child(ren) is the one with legal custody. NY Courts have agreed that joint custody may be appropriate where the parents consent, but is largely given to one parent after a contested hearing.

Custody is not an automatic right in either parent. Instead, the court must determine custody disputes only according to what is in the best interest of the child(ren). In determining what is in the best interest of the child(ren), the court considers the totality of the circumstances including but not limited to:

1. Each parent's age
2. Each parent's physical and mental health. To the extent is materially affects the parent's ability to care for the child, the parent's physical disability will be considered by the court among the other factors in the custody determination.
3. Each parent's ability to provide for the child. Often child support will be used to relieve financial disparity. However financial ability is not a significant factor.
4. The quality of care each parent can provide. The court seems to fabor giving custody to the parent who can spend more time with the child rather than havingto rely on others to take care of the child because (s)he is often unavailsble. Pawelski v. Bucholtz, 91 A.D.2d 1200 (1983).
5. Child(ren)'s current lifestyle
6. Child(ren)'s current living situation
7. Whether child(ren) will be separated from siblings. Eschbach v. Eschbach, 56 N.Y.2d 167 (1982)
8. Child(ren)'s preference (depending on age). A court will consider the chil(ren)'s preference but is not bound by it. In determining how much weight to give it, the court must consider the age, maturity, and consider the possibility of parental influence. Eschbach v. Eschbach. However, a court may disregard the child's preference when opposed to the child's best interest.
9. Child(ren)'s relationship with each parent
10. Instances of abuse or domestic violence. See Domestic Relations Law 240.1
12. Alcohol and drug abuse. Although a mother had an  issue with alcoholism, she was improving and the court found that she was in a better position to have custody as opposed to the 74 year old father who had no meaningful interaction wtih the child. Worowski v. Worowski, 95 A.D.2d 687 (1983).
13. Existing agreements or informal agreements relating to custody. Bishop v. Lansley, 106 A.D.2d 732 (1984) suggested that where children lived with the petitioner for a long peeriod of time and where there was no indication that a change would enhance their well being, continuing the status quo was in their best interests. Adams v. Franklin, 9 A.D.3d 544 (2004) held the court must consider the duration of the present custody agreement. The longer the agreement the more weight it's given as courts assume that the parties by their longstanding actions already made the custody determination.
14. Findings of child neglect/abuse
15. Each parent's observable behavior in court
16. Willingness to foster the Child(ren)'s Relationship with the Other Parent. The court will give great weight to a parent's nurturing and encouragement of the relationship between the child and other parent as well as to the parent's intereference with that relationship.  Walden v. Walden, 112 A.D.2d 1035 (1985). It is possible for the parent's interference alone to provide sufficient basis to consider changing an existing custody order in light of the totality of the circumstances. Juneau v. Juneau 240 A.D.2d 858 (3rd Dept. 1997), Frank R. v. Deborah Ann R. 204 A.D.2d 615 (1994), Eastman v. Drennen, 122 A.D.2d 397 (3rd Dept. 1986).
17. Home environment. Plays a significant role in deciding custody. Eschbach v. Eschbach. In Royea v. Hutchings, 260 A.D.2d 678 (3rd Dept. 1999), the father won custody when the court found that the mother's home had become stressful and chaotic, and that the child was not thriving under those circumstances. In Ingalls v. Ingalls 58 A.D.2d 1039 (4th Dept 1977), where mother's relationship with her boyfriend involved quarrels and disturbances, and where the home was unheated on one or more occasion, the father was granted custody. Where neither home environment is bad, the court often has to choose the better of both. Sooy v. Sooy, 101 A.D.2d 287 (3d Dep't, 1984).

The court often looks at past actions of the parties to assist it in determining the parties' future actions with respect to the best interest of the child(ren). Additionally, a court may use expert testimony in its determination. A law guardian will be assigned by the court to represent the interests of the child and to take a position on custody supported by the evidence on the record.

Modification
The party seeking to modify the custody arrangement must first show a significant and sufficient change in circumstances and, if the sufficient change is shown, that the modification would be in the best interests of the child(ren). Grassi v. Grassi, 28 A.D.3d 482 (2006); McNally v. McNally, 28 A.D.3d 526 (2006).

The party seeking a change is custody is not automatically entitled to a hearing unless (s)he can make an evidentiary showing sufficient to warrant one. Teuschker v. Teuschler, 242 A.D.2d 289 (1997); accord Spratt v. Fontana, 46 A.D.3d 670 (2007).

Relocation of the Custodial Parent
A leading case is Tropea v. Tropea, 87 N.Y.2d 727 (1996) where in, view of the best interests standard, the Court of Appeals seems to increase the ability of the custodial parent to move considering that "(l)ike Humpty Dumpty, a family, once broken by divorce, cannot be put back together in precisely the same way. The relationship between the parents and the children is necessarily different after a divorce and, accordingly, it may be unrealistic in some cases to try to preserve the noncustodial parent's accustomed close involvement in the children's everyday life at the expense of the custodial parent's efforts to start a new life or to form a new family unit. In some cases, the child's interests might be better served by fashioning visitation plans that maximize the noncustodial parent's opportunity to maintain a positive nurturing relationship while enabling the custodial parent, who has the primary child-rearing responsibility, to go forward with his or her life. In any event, it serves neither the interests of the children nor the ends of justice to view relocation cases through the prisms of presumptions and threshold tests that artificially skew the analysis in favor of one outcome or another." Id.

In seeking to move with the child to another city, state etc., the custodial parent bears the burden of proving by a preponderance of the evidence that the proposed relocation is in the best interests of the child(ren). Matter of Winn v. Cutting, 39 A.D.3d 1000 (2007); Matter of Willis-Marsh v. Wilkerson, 22 A.D.3d 977 (2005). However, NY generally gives deference to the custodial parent's decision to move so long as the reason for the move is not to defeat the non-custodial parent's right of access to the child. Additionally, where the relocation does not deprive the non-custodial parent of meaningful access to the child(ren), the moving parent is not required to show exceptional circumstances to justify the relocation. See Matter of Browner v. Kenward, 213 A.D.2d 400 (1995).

In deciding relocation disputes, the court will consider:
1. The parties' reasons for seeking/opposing relocation
2. Each parent's relationship with the child
3. Impact of move on quantity and quality of the child's future contact with the non-custodial parent
4. Degree to which the custodial parent's and child's life could be enhanced by the move
5. Feasibility of preserving the relationship between the child and non-custodial parent using suitable visitation arrangements
6. The harm that may ensue if the move is not permitted

It's also possible, of course depending on the facts and in light of the best interests of the child, that the court would entertain or even suggest a transfer of custody or a parrllel move by the non-custodial parent.

New Jersey