 Armatures, or skeletons, can be very powerful, but they can also get very messy. If you have a very complex rig, with different deform bones, controllers, constraint specific bones, etc, etc, you'll want to start hiding certain bones or selectively viewing others so that you only see the bones you need at any given moment. This is where bone layers come into play. Instead of manually hiding and unhiding bones as you work, you can actually place bones in certain bone layers within your armature, allowing you to selectively view any given bone layer or layers at any time. This works differently from collections as there is a maximum of 32 layers, but often times that is more than enough. I'm going to demonstrate bone layers on a simple rig, but just remember bone layers are most often used on complex rigs where organization is necessary for clarity. We can see the bone layers visually in the Armature Properties tab in our Properties Editor. This tab is indicated by a green stick figure icon. Once there, you can see this horizontal grid-like pattern which represents our bone layers. You don't have to count them, but there are 32 squares displayed here horizontally. The other 32 squares you see right below the layer section is for selecting which layers from above will be considered protected layers. They're technically still referencing the same 32 layers we see up here, but we'll come back to this section later. Clicking on a square in the grid will enable that layer exclusively, hiding all bones on all other bone layers. Holding Shift and Left Clicking on another square will allow you to toggle on or off multiple bone layers at a time. You might notice that the first square here has a small white dot in the middle. This represents the fact that there are bones within that layer, and typically enabling that layer will make these bones visible. By default, our bones exist on our first layer, and our first layer is already enabled. Now that you understand that, let's get to organizing. You can choose to organize your bones however you want, but let's say for our sake, we want to simply move our bones of each limb in our rig to separate layers, while still keeping the rest of the rig in the first default layer. So to accomplish this, we'll need five layers total, including our first layer. Let's choose five layers that'll make sense visually in our bone layers grid pattern. I'm going to choose these two for our left and right arm bones, and these two for our left and right leg bones. This way, I know that the top layer is generally for left hand side bones, and the bottom layer is for right hand side bones. Now let's move our bones where they need to go. I'm going to start with the left arm bones. To move our bones to a different bone layer, simply go into pose mode, select the bones you want to move, and go to the pose menu at the top left of our viewport. You can then select change bone layer. This will pop up a menu that looks exactly like our layer grid that we saw in our properties editor. For hotkey users, simply hover over anywhere in the viewport and press the M key as in move to bring up the same layer menu. Now you can simply select the layer or layers you would like your selected bones to reside in. For the left arm bones, we decided to place them here in the second layer of the top row. Once we do that, you can see that our bones have disappeared from our viewport as they are now hidden in the second bone layer while we still only have the first bone layer enabled. Let's repeat this process for our other limbs. Now that we have our bones in the right layers, we can select these layers with left click to see each limbs bones independently or shift select to enable multiple bone layers at a time. You may have already noticed that only one square in the grid pattern actually has a filled white dot while the others have a hollow white dot. The filled in white dot simply indicates which layer your last selected bone or active bone is on while the hollow white dots simply indicate that there are bones present in that layer. And those are the basics of bone layers but we haven't touched on what this protected layers section does exactly. For most beginners, you probably won't have to touch these settings as they refer specifically to when the rig is imported into other blender files and referenced as a proxy. Protecting a layer tells proxy rigs of the source that bones on that layer should prioritize and reference the original data from the source file if the source changes. Referencing files is most common in studio environments or group productions. And those are the fundamentals for bone layers but for further organization I also recommend bone groups. What are bone groups? Well, let me just show you real quick. Bone groups can be edited right below the bone layers in the armature properties of our properties editor. Expand that and you'll see a very familiar interface if you've worked with vertex groups already. To create a new bone group simply press the plus key. Double left clicking a group will allow you to rename the group to whatever you want. I'm going to call this left. And now since you probably know what I'm going to do, let's create another group called right. We can add bones to whatever group we have selected in this list by simply going into pose mode, selecting what bones we want, and clicking the assign button in the bone groups interface in our armature properties. I'm going to go ahead and organize these bones so that the left hand side bones are assigned to the left group and the right hand side bones are assigned to the right group. Okay, now that I've done that, let's go ahead and deselect everything with Alt A. Now what's great about bone groups is that we can very easily select or deselect bones in that group by selecting the group in that list and clicking the select or deselect buttons here. But another great benefit of bone groups is colors for visual clarity. What I love to do for example is to mark our left hand side bones as red and our right hand side bones as blue. How do we do this? Well, you can simply select our left group and go to the color drop down below. From this, we can select a color set that matches what we want or we can create a custom color set. When setting custom colors, you can read more about what each color is used for by hovering over each colored rectangle. Let's do the same thing for the right group. Now we have this very colorful rig that helps us and whoever animates with this rig understand at a glance which bones belong to which groups. Important note, unlike vertex groups, bones can only belong to one bone group at a time. I hope you find these tools useful for understanding and organizing the bones within your rigs.