A holster for receiving a handgun having a handgun body a handgrip, a slide, and a trigger guard, the holster comprising: a holster body having a plurality of unitary holster wall portions defining a handgun receiving cavity and a rearward opening, the holster body having a handgun receiving and withdrawal axis, the plurality of holster wall portions comprising a user proximal wall portion and a user distal wall portion, the proximal wall portion having a thumb button recess with a thumb button edge portion defining the thumb button recess, the thumb button recess extending forwardly from the rearward opening; a first user actuatable handgun retention mechanism at the proximal wall portion for selectively preventing the handgun, when in the cavity, from being withdrawn from the cavity; the first handgun retention mechanism comprising a first lever pivotally mounted on the proximal wall portion of the holster body with a first axis of rotation, the first lever having an actuation tab rearwardly positioned on the lever and positioned within the recess, the actuation tab having an upper margin, a rearward margin, and a lower margin, the lever further having a trigger guard blocking portion forwardly positioned on the lever, the lever configured and positioned such that depression of the actuation tab rotates the lever about its respective axis of rotation to move the trigger guard blocking portion from a trigger guard blocking position to a non-blocking position, wherein the first lever is seated in a lever receiving region on the proximal wall portion and has two unitary pivot portions that cooperate with two pivot portions unitary with the proximal wall portion, whereby the pivoting connection is made without metal pins; wherein an upper portion of the thumb button recess edge portion extends rearwardly of the actuation tab along the upper margin of the actuation tab and a lower portion of the thumb button recess edge portion extends rearwardly of the actuation tab at the lower margin of the actuation tab. a holster body having a plurality of unitary holster wall portions defining a handgun receiving cavity and a rearward opening, the holster body having a handgun receiving and withdrawal axis, the plurality of holster wall portions comprising a user proximal wall portion and a user distal wall portion, the proximal wall portion having a thumb button recess with a thumb button edge portion defining the thumb button recess, the thumb button recess extending forwardly from the rearward opening; a first user actuatable handgun retention mechanism at the proximal wall portion for selectively preventing the handgun, when in the cavity, from being withdrawn from the cavity; the first handgun retention mechanism comprising a first lever pivotally mounted on the proximal wall portion of the holster body with a first axis of rotation, the first lever having an actuation tab rearwardly positioned on the lever and positioned within the recess, the actuation tab having an upper margin, a rearward margin, and a lower margin, the lever further having a trigger guard blocking portion forwardly positioned on the lever, the lever configured and positioned such that depression of the actuation tab rotates the lever about its respective axis of rotation to move the trigger guard blocking portion from a trigger guard blocking position to a non-blocking position, wherein the first lever is seated in a lever receiving region on the proximal wall portion and has two unitary pivot portions that cooperate with two pivot portions unitary with the proximal wall portion, whereby the pivoting connection is made without metal pins; wherein an upper portion of the thumb button recess edge portion extends rearwardly of the actuation tab along the upper margin of the actuation tab and a lower portion of the thumb button recess edge portion extends rearwardly of the actuation tab at the lower margin of the actuation tab.