How to set iPhone UI View z index?

UIView siblings are stacked in the order in which they are added to their superview. The UIViewhierarchy methods and properties are there to manage view order. In UIView.h:

-(void)insertSubview:(UIView*)view atIndex:(NSInteger)index;
-(void)exchangeSubviewAtIndex:(NSInteger)index1 withSubviewAtIndex:(NSInteger)index2;
-(void)insertSubview:(UIView*)view belowSubview:(UIView*)siblingSubview;
-(void)insertSubview:(UIView*)view aboveSubview:(UIView*)siblingSubview;

The sibling views are ordered back to front in the subviews array. So the topmost view will be:

[parentView.subviews lastObject];

and bottom view will be:

[parentView.subviews objectAtIndex:0];

Like Kolin Krewinkel said, [parentView bringSubviewToFront:view] will bring the view to the top, but this is only the case if the views are all siblings in the hierarchy.