diff --git a/basic-geometry/matrix2x2.c b/basic-geometry/matrix2x2.c
index bb0e5c1..0f4927b 100644
--- a/basic-geometry/matrix2x2.c
+++ b/basic-geometry/matrix2x2.c
@@ -18,6 +18,9 @@ extern inline double bgc_matrix2x2_get_determinant_fp64(const BgcMatrix2x2FP64*
 extern inline int bgc_matrix2x2_is_singular_fp32(const BgcMatrix2x2FP32* matrix);
 extern inline int bgc_matrix2x2_is_singular_fp64(const BgcMatrix2x2FP64* matrix);
 
+extern inline int bgc_matrix2x2_is_rotation_fp32(const BgcMatrix2x2FP32* matrix);
+extern inline int bgc_matrix2x2_is_rotation_fp64(const BgcMatrix2x2FP64* matrix);
+
 extern inline void bgc_matrix2x2_copy_fp32(const BgcMatrix2x2FP32* source, BgcMatrix2x2FP32* destination);
 extern inline void bgc_matrix2x2_copy_fp64(const BgcMatrix2x2FP64* source, BgcMatrix2x2FP64* destination);
 
diff --git a/basic-geometry/matrix2x2.h b/basic-geometry/matrix2x2.h
index ad46eff..6bf6541 100644
--- a/basic-geometry/matrix2x2.h
+++ b/basic-geometry/matrix2x2.h
@@ -109,6 +109,32 @@ inline int bgc_matrix2x2_is_singular_fp64(const BgcMatrix2x2FP64* matrix)
     return bgc_is_zero_fp64(bgc_matrix2x2_get_determinant_fp64(matrix));
 }
 
+// ================ Is Rotation ================= //
+
+inline int bgc_matrix2x2_is_rotation_fp32(const BgcMatrix2x2FP32* matrix)
+{
+    const float product_r1c1 = matrix->r1c1 * matrix->r1c1 + matrix->r1c2 * matrix->r2c1;
+    const float product_r1c2 = matrix->r1c1 * matrix->r1c2 + matrix->r1c2 * matrix->r2c2;
+
+    const float product_r2c1 = matrix->r2c1 * matrix->r1c1 + matrix->r2c2 * matrix->r2c1;
+    const float product_r2c2 = matrix->r2c1 * matrix->r1c2 + matrix->r2c2 * matrix->r2c2;
+
+    return bgc_is_unit_fp32(product_r1c1) && bgc_is_zero_fp32(product_r1c2)
+        && bgc_is_zero_fp32(product_r2c1) && bgc_is_unit_fp32(product_r2c2);
+}
+
+inline int bgc_matrix2x2_is_rotation_fp64(const BgcMatrix2x2FP64* matrix)
+{
+    const double product_r1c1 = matrix->r1c1 * matrix->r1c1 + matrix->r1c2 * matrix->r2c1;
+    const double product_r1c2 = matrix->r1c1 * matrix->r1c2 + matrix->r1c2 * matrix->r2c2;
+
+    const double product_r2c1 = matrix->r2c1 * matrix->r1c1 + matrix->r2c2 * matrix->r2c1;
+    const double product_r2c2 = matrix->r2c1 * matrix->r1c2 + matrix->r2c2 * matrix->r2c2;
+
+    return bgc_is_unit_fp64(product_r1c1) && bgc_is_zero_fp64(product_r1c2)
+        && bgc_is_zero_fp64(product_r2c1) && bgc_is_unit_fp64(product_r2c2);
+}
+
 // ==================== Copy ==================== //
 
 inline void bgc_matrix2x2_copy_fp32(const BgcMatrix2x2FP32* source, BgcMatrix2x2FP32* destination)
diff --git a/basic-geometry/matrix3x3.c b/basic-geometry/matrix3x3.c
index a67f481..fc61d36 100644
--- a/basic-geometry/matrix3x3.c
+++ b/basic-geometry/matrix3x3.c
@@ -24,6 +24,9 @@ extern inline double bgc_matrix3x3_get_determinant_fp64(const BgcMatrix3x3FP64*
 extern inline int bgc_matrix3x3_is_singular_fp32(const BgcMatrix3x3FP32* matrix);
 extern inline int bgc_matrix3x3_is_singular_fp64(const BgcMatrix3x3FP64* matrix);
 
+extern inline int bgc_matrix3x3_is_rotation_fp32(const BgcMatrix3x3FP32* matrix);
+extern inline int bgc_matrix3x3_is_rotation_fp64(const BgcMatrix3x3FP64* matrix);
+
 extern inline void bgc_matrix3x3_transpose_fp32(const BgcMatrix3x3FP32* matrix, BgcMatrix3x3FP32* transposed);
 extern inline void bgc_matrix3x3_transpose_fp64(const BgcMatrix3x3FP64* matrix, BgcMatrix3x3FP64* transposed);
 
diff --git a/basic-geometry/matrix3x3.h b/basic-geometry/matrix3x3.h
index c1ab5c2..a716d67 100644
--- a/basic-geometry/matrix3x3.h
+++ b/basic-geometry/matrix3x3.h
@@ -272,6 +272,46 @@ inline int bgc_matrix3x3_is_singular_fp64(const BgcMatrix3x3FP64* matrix)
     return bgc_is_zero_fp64(bgc_matrix3x3_get_determinant_fp64(matrix));
 }
 
+// ================ Is Rotation ================= //
+
+inline int bgc_matrix3x3_is_rotation_fp32(const BgcMatrix3x3FP32* matrix)
+{
+    const float product_r1c1 = matrix->r1c1 * matrix->r1c1 + matrix->r1c2 * matrix->r2c1 + matrix->r1c3 * matrix->r3c1;
+    const float product_r1c2 = matrix->r1c1 * matrix->r1c2 + matrix->r1c2 * matrix->r2c2 + matrix->r1c3 * matrix->r3c2;
+    const float product_r1c3 = matrix->r1c1 * matrix->r1c3 + matrix->r1c2 * matrix->r2c3 + matrix->r1c3 * matrix->r3c3;
+
+    const float product_r2c1 = matrix->r2c1 * matrix->r1c1 + matrix->r2c2 * matrix->r2c1 + matrix->r2c3 * matrix->r3c1;
+    const float product_r2c2 = matrix->r2c1 * matrix->r1c2 + matrix->r2c2 * matrix->r2c2 + matrix->r2c3 * matrix->r3c2;
+    const float product_r2c3 = matrix->r2c1 * matrix->r1c3 + matrix->r2c2 * matrix->r2c3 + matrix->r2c3 * matrix->r3c3;
+
+    const float product_r3c1 = matrix->r3c1 * matrix->r1c1 + matrix->r3c2 * matrix->r2c1 + matrix->r3c3 * matrix->r3c1;
+    const float product_r3c2 = matrix->r3c1 * matrix->r1c2 + matrix->r3c2 * matrix->r2c2 + matrix->r3c3 * matrix->r3c2;
+    const float product_r3c3 = matrix->r3c1 * matrix->r1c3 + matrix->r3c2 * matrix->r2c3 + matrix->r3c3 * matrix->r3c3;
+
+    return bgc_is_unit_fp32(product_r1c1) && bgc_is_zero_fp32(product_r1c2) && bgc_is_zero_fp32(product_r1c3)
+        && bgc_is_zero_fp32(product_r2c1) && bgc_is_unit_fp32(product_r2c2) && bgc_is_zero_fp32(product_r2c3)
+        && bgc_is_zero_fp32(product_r3c1) && bgc_is_zero_fp32(product_r3c2) && bgc_is_unit_fp32(product_r3c3);
+}
+
+inline int bgc_matrix3x3_is_rotation_fp64(const BgcMatrix3x3FP64* matrix)
+{
+    const double product_r1c1 = matrix->r1c1 * matrix->r1c1 + matrix->r1c2 * matrix->r2c1 + matrix->r1c3 * matrix->r3c1;
+    const double product_r1c2 = matrix->r1c1 * matrix->r1c2 + matrix->r1c2 * matrix->r2c2 + matrix->r1c3 * matrix->r3c2;
+    const double product_r1c3 = matrix->r1c1 * matrix->r1c3 + matrix->r1c2 * matrix->r2c3 + matrix->r1c3 * matrix->r3c3;
+
+    const double product_r2c1 = matrix->r2c1 * matrix->r1c1 + matrix->r2c2 * matrix->r2c1 + matrix->r2c3 * matrix->r3c1;
+    const double product_r2c2 = matrix->r2c1 * matrix->r1c2 + matrix->r2c2 * matrix->r2c2 + matrix->r2c3 * matrix->r3c2;
+    const double product_r2c3 = matrix->r2c1 * matrix->r1c3 + matrix->r2c2 * matrix->r2c3 + matrix->r2c3 * matrix->r3c3;
+
+    const double product_r3c1 = matrix->r3c1 * matrix->r1c1 + matrix->r3c2 * matrix->r2c1 + matrix->r3c3 * matrix->r3c1;
+    const double product_r3c2 = matrix->r3c1 * matrix->r1c2 + matrix->r3c2 * matrix->r2c2 + matrix->r3c3 * matrix->r3c2;
+    const double product_r3c3 = matrix->r3c1 * matrix->r1c3 + matrix->r3c2 * matrix->r2c3 + matrix->r3c3 * matrix->r3c3;
+
+    return bgc_is_unit_fp64(product_r1c1) && bgc_is_zero_fp64(product_r1c2) && bgc_is_zero_fp64(product_r1c3)
+        && bgc_is_zero_fp64(product_r2c1) && bgc_is_unit_fp64(product_r2c2) && bgc_is_zero_fp64(product_r2c3)
+        && bgc_is_zero_fp64(product_r3c1) && bgc_is_zero_fp64(product_r3c2) && bgc_is_unit_fp64(product_r3c3);
+}
+
 // =================== Invert =================== //
 
 int bgc_matrix3x3_invert_fp32(const BgcMatrix3x3FP32* matrix, BgcMatrix3x3FP32* inverted);
diff --git a/basic-geometry/slerp.c b/basic-geometry/slerp.c
index b318059..2e03264 100644
--- a/basic-geometry/slerp.c
+++ b/basic-geometry/slerp.c
@@ -3,8 +3,8 @@
 extern inline void bgc_slerp_reset_fp32(BgcSlerpFP32* slerp);
 extern inline void bgc_slerp_reset_fp64(BgcSlerpFP64* slerp);
 
-extern inline bgc_slerp_get_turn_for_phase_fp32(const BgcSlerpFP32* slerp, const float phase, BgcVersorFP32* result);
-extern inline bgc_slerp_get_turn_for_phase_fp64(const BgcSlerpFP64* slerp, const double phase, BgcVersorFP64* result);
+extern inline void bgc_slerp_get_turn_for_phase_fp32(const BgcSlerpFP32* slerp, const float phase, BgcVersorFP32* result);
+extern inline void bgc_slerp_get_turn_for_phase_fp64(const BgcSlerpFP64* slerp, const double phase, BgcVersorFP64* result);
 
 void bgc_slerp_make_full_fp32(const BgcVersorFP32* start, const BgcVersorFP32* end, BgcSlerpFP32* slerp)
 {
diff --git a/basic-geometry/slerp.h b/basic-geometry/slerp.h
index 9289008..a4a2053 100644
--- a/basic-geometry/slerp.h
+++ b/basic-geometry/slerp.h
@@ -61,7 +61,7 @@ void bgc_slerp_make_shortened_fp32(const BgcVersorFP32* start, const BgcVersorFP
 
 void bgc_slerp_make_shortened_fp64(const BgcVersorFP64* start, const BgcVersorFP64* end, BgcSlerpFP64* slerp);
 
-inline bgc_slerp_get_turn_for_phase_fp32(const BgcSlerpFP32* slerp, const float phase, BgcVersorFP32* result)
+inline void bgc_slerp_get_turn_for_phase_fp32(const BgcSlerpFP32* slerp, const float phase, BgcVersorFP32* result)
 {
     const float angle = slerp->radians * phase;
     const float cosine = cosf(angle);
@@ -76,7 +76,7 @@ inline bgc_slerp_get_turn_for_phase_fp32(const BgcSlerpFP32* slerp, const float
     );
 }
 
-inline bgc_slerp_get_turn_for_phase_fp64(const BgcSlerpFP64* slerp, const double phase, BgcVersorFP64* result)
+inline void bgc_slerp_get_turn_for_phase_fp64(const BgcSlerpFP64* slerp, const double phase, BgcVersorFP64* result)
 {
     const double angle = slerp->radians * phase;
     const double cosine = cos(angle);