diff --git a/.changeset/typography-scale-headings.md b/.changeset/typography-scale-headings.md
new file mode 100644
index 0000000000..e3b3fc2567
--- /dev/null
+++ b/.changeset/typography-scale-headings.md
@@ -0,0 +1,20 @@
+---
+"@cloudoperators/juno-ui-components": minor
+---
+
+Add h1–h6 base typography styles aligned with the Juno design system scale.
+
+- `global.css` and `theme.css`: h1–h6 defined in `@layer base` with IBM Plex Sans Bold, rem font sizes, and plain CSS `line-height` values. `theme.css` uses `var(--font-sans)` instead of a hardcoded font stack.
+- `FormattedText`: heading sizes and line-heights aligned with the scale; h5 corrected (1.03rem → 1.125rem); h6 added; redundant `font-weight`/`font-style` declarations removed.
+- `ContentHeading`: removed `jn:font-bold` and `jn:text-lg` overrides that were overriding the h1 base style with a smaller size.
+
+Fix h1 misuse in components that rendered UI labels as `<h1>`, which caused unintended size changes after the global h1 style was introduced. Heading levels were chosen to reflect both visual size and accessibility (correct heading outline for screen readers).
+
+- `Modal`: title changed from `<h1>` to `<h4>`. The modal has `role="dialog"` which creates an isolated landmark; the title is referenced via `aria-labelledby`. A heading inside a dialog is semantically correct and independent of the page outline. `<h4>` matches the previous visual size (~20px).
+- `Form`: title changed from `<h1>` to `<h3>`. A form is a named content section; a heading is appropriate. `<h3>` matches the previous visual size (~24px).
+- `FormSection`: title changed from `<h1>` to `<h4>`. One level below `Form` (`<h3>`) in the heading hierarchy. `<h4>` was chosen over `<h5>` (visual match) to maintain correct nesting.
+- `SignInForm`: title changed from `<h1>` to `<h2>`. The form is often the primary content of a page but may also be embedded; `<h2>` is a safe default for both cases.
+- `IntroBox`: title changed from `<h1>` to `<p>`. An info box is not a navigable section; adding it to the heading outline would confuse screen reader users navigating by heading. Bold styling preserved via existing `introboxHeading` class.
+- `global.css`: replaced `font-weight: 700` with `@apply jn:font-bold` in h1–h6 base styles for consistency with Tailwind conventions.
+- `theme.css`: same — replaced `font-weight: 700` with `@apply font-bold` (no `jn:` prefix, consistent with existing `@apply` usage in that file).
+- `Modal`: ReactNode titles now render as `<div role="heading" aria-level={4}>` instead of `<h4>` to avoid invalid HTML (block elements inside heading elements). String titles remain `<h4>`. Both approaches are equivalent for assistive technologies.
diff --git a/packages/ui-components/src/components/ContentHeading/ContentHeading.component.tsx b/packages/ui-components/src/components/ContentHeading/ContentHeading.component.tsx
index 87aaf3a080..cf22f9c7d1 100644
--- a/packages/ui-components/src/components/ContentHeading/ContentHeading.component.tsx
+++ b/packages/ui-components/src/components/ContentHeading/ContentHeading.component.tsx
@@ -6,8 +6,6 @@
 import React, { HTMLAttributes, ReactNode } from "react"
 
 const baseHeadingStyles = `
-  jn:font-bold
-  jn:text-lg
   jn:text-theme-high
   jn:pb-2
 `
diff --git a/packages/ui-components/src/components/Form/Form.component.tsx b/packages/ui-components/src/components/Form/Form.component.tsx
index e6b610b800..b252ede711 100644
--- a/packages/ui-components/src/components/Form/Form.component.tsx
+++ b/packages/ui-components/src/components/Form/Form.component.tsx
@@ -10,8 +10,6 @@ const formBaseStyles = `
 `
 
 const formTitleStyles = `
-  jn:text-2xl
-  jn:font-bold
   jn:mb-4
 `
 
@@ -45,7 +43,7 @@ export interface FormProps extends FormHTMLAttributes<HTMLFormElement> {
 export const Form = ({ title = "", className = "", children, ...props }: FormProps): ReactNode => {
   return (
     <form className={`juno-form ${formBaseStyles} ${className}`} {...props}>
-      {title ? <h1 className={`juno-form-heading ${formTitleStyles}`}>{title}</h1> : null}
+      {title ? <h3 className={`juno-form-heading ${formTitleStyles}`}>{title}</h3> : null}
       {children}
     </form>
   )
diff --git a/packages/ui-components/src/components/FormSection/FormSection.component.tsx b/packages/ui-components/src/components/FormSection/FormSection.component.tsx
index 38f160985e..df39d46e60 100644
--- a/packages/ui-components/src/components/FormSection/FormSection.component.tsx
+++ b/packages/ui-components/src/components/FormSection/FormSection.component.tsx
@@ -11,8 +11,6 @@ const formSectionBaseStyles = `
 `
 
 const headingStyles = `
-    jn:text-lg
-    jn:font-bold
     jn:mb-4
 `
 
@@ -45,7 +43,7 @@ export interface FormSectionProps extends HTMLAttributes<HTMLElement> {
 export const FormSection = ({ title = "", children, className = "", ...props }: FormSectionProps): ReactNode => {
   return (
     <section className={`juno-form-section ${formSectionBaseStyles} ${className}`} {...props}>
-      {title ? <h1 className={`juno-formsection-heading ${headingStyles}`}>{title}</h1> : null}
+      {title ? <h4 className={`juno-formsection-heading ${headingStyles}`}>{title}</h4> : null}
       {children}
     </section>
   )
diff --git a/packages/ui-components/src/components/FormattedText/formatted-text.css b/packages/ui-components/src/components/FormattedText/formatted-text.css
index 68d5bddfec..0ef051be29 100644
--- a/packages/ui-components/src/components/FormattedText/formatted-text.css
+++ b/packages/ui-components/src/components/FormattedText/formatted-text.css
@@ -36,42 +36,40 @@
 
   h1 {
     font-size: 1.69rem;
-    font-weight: 700;
-    line-height: 1.11; /* round(40 / 36) */
+    line-height: 1.375;
     margin-top: 0;
     margin-bottom: 2rem; /* rem(32) */
   }
 
   h2 {
     font-size: 1.56rem;
-    font-weight: 700;
-    line-height: 160%;
+    line-height: 1.375;
     margin-top: 3rem; /* rem(48) */
     margin-bottom: 1.5rem; /* rem(24) */
   }
 
   h3 {
     font-size: 1.44rem;
-    font-weight: 700;
-    line-height: 160%;
+    line-height: 1.375;
     margin-top: 1rem;
     margin-bottom: 0.75rem; /* rem(12) */
   }
 
   h4 {
     font-size: 1.28rem;
-    font-style: normal;
-    font-weight: 700;
-    line-height: 160%;
+    line-height: 1.625;
     margin-top: 1.5rem; /* rem(24) */
     margin-bottom: 0.5rem; /* rem(8) */
   }
 
   h5 {
-    font-size: 1.03rem;
-    font-style: normal;
-    font-weight: 700;
-    line-height: 160%;
+    font-size: 1.125rem;
+    line-height: 1.625;
+  }
+
+  h6 {
+    font-size: 1rem;
+    line-height: 1.5;
   }
 
   img,
diff --git a/packages/ui-components/src/components/IntroBox/IntroBox.component.tsx b/packages/ui-components/src/components/IntroBox/IntroBox.component.tsx
index 0a719dddab..776519aa57 100644
--- a/packages/ui-components/src/components/IntroBox/IntroBox.component.tsx
+++ b/packages/ui-components/src/components/IntroBox/IntroBox.component.tsx
@@ -119,7 +119,7 @@ export const IntroBox = ({
     >
       <div className={`${introboxBorder}`}></div>
       <div className={`${introboxContent(variant, heroImage)}`}>
-        {title ? <h1 className={`${introboxHeading}`}>{title}</h1> : ""}
+        {title ? <p className={`${introboxHeading}`}>{title}</p> : ""}
         {children ? children : <p>{text}</p>}
       </div>
     </div>
diff --git a/packages/ui-components/src/components/Message/Message.component.tsx b/packages/ui-components/src/components/Message/Message.component.tsx
index 47294c3dbc..990406fcca 100644
--- a/packages/ui-components/src/components/Message/Message.component.tsx
+++ b/packages/ui-components/src/components/Message/Message.component.tsx
@@ -264,7 +264,7 @@ export const Message = ({
       <div className={`juno-message-border ${messageBorderStyles} ${variantStyle}`}></div>
       <Icon icon={iconToRender} size={21} className={`${getIconStyles(variant)} ${messageIconStyles}`} />
       <div className={`juno-message-content ${messageContentStyles}`}>
-        {title && <h1 className={messageHeadingStyles}>{title}</h1>}
+        {title && <strong className={messageHeadingStyles}>{title}</strong>}
         <div>{children || text}</div>
       </div>
       {dismissible && (
diff --git a/packages/ui-components/src/components/Modal/Modal.component.tsx b/packages/ui-components/src/components/Modal/Modal.component.tsx
index 71839c3e5d..327487bbe1 100644
--- a/packages/ui-components/src/components/Modal/Modal.component.tsx
+++ b/packages/ui-components/src/components/Modal/Modal.component.tsx
@@ -57,7 +57,9 @@ const headerstyles = `
 `
 
 const titlestyles = `
-  jn:text-xl
+  jn:font-sans
+  jn:text-[1.28rem]
+  jn:leading-relaxed
   jn:font-bold
 `
 
@@ -177,13 +179,13 @@ export const Modal = ({
     }
     if (typeof modalTitle === "string") {
       return (
-        <h1 className={`juno-modal-title ${titlestyles}`} id={modalTitleId}>
+        <h4 className={`juno-modal-title ${titlestyles}`} id={modalTitleId}>
           {modalTitle}
-        </h1>
+        </h4>
       )
     }
     return (
-      <div className={`juno-modal-title ${titlestyles}`} id={modalTitleId}>
+      <div className={`juno-modal-title ${titlestyles}`} role="heading" aria-level={4} id={modalTitleId}>
         {modalTitle}
       </div>
     )
diff --git a/packages/ui-components/src/components/Modal/Modal.test.tsx b/packages/ui-components/src/components/Modal/Modal.test.tsx
index 30034466f9..f3b9306703 100644
--- a/packages/ui-components/src/components/Modal/Modal.test.tsx
+++ b/packages/ui-components/src/components/Modal/Modal.test.tsx
@@ -53,7 +53,7 @@ describe("Modal", () => {
     )
 
     const dialog = screen.getByRole("dialog")
-    const titleWrapper = screen.getByText("Node Title").closest("div")
+    const titleWrapper = screen.getByRole("heading", { level: 4 })
 
     expect(dialog).toBeInTheDocument()
     expect(titleWrapper).toBeInTheDocument()
diff --git a/packages/ui-components/src/components/PopupMenu/PopupMenu.component.tsx b/packages/ui-components/src/components/PopupMenu/PopupMenu.component.tsx
index ca657b0cfe..9c40e50799 100644
--- a/packages/ui-components/src/components/PopupMenu/PopupMenu.component.tsx
+++ b/packages/ui-components/src/components/PopupMenu/PopupMenu.component.tsx
@@ -398,7 +398,7 @@ export const PopupMenuSectionHeading = ({
 }: PopupMenuSectionHeadingProps): ReactNode => {
   return (
     <header className={`juno-popupmenu-section-title ${sectionTitleStyles} ${className}`} {...props}>
-      <h1>{label && label.length ? label : children}</h1>
+      {label && label.length ? label : children}
     </header>
   )
 }
diff --git a/packages/ui-components/src/components/SignInForm/SignInForm.component.tsx b/packages/ui-components/src/components/SignInForm/SignInForm.component.tsx
index 469ee20ce1..c813fae5d2 100644
--- a/packages/ui-components/src/components/SignInForm/SignInForm.component.tsx
+++ b/packages/ui-components/src/components/SignInForm/SignInForm.component.tsx
@@ -8,8 +8,6 @@ import { Message } from "../Message"
 import { Stack } from "../Stack"
 
 const signInFormTitleStyles = `
-  jn:text-xl
-  jn:font-bold
   jn:text-theme-highest
   jn:mb-4
 `
@@ -75,7 +73,7 @@ export const SignInForm = ({
 
   return (
     <form className={`juno-sign-in-form ${className}`} {...props}>
-      {title !== false && <h1 className={`juno-sign-in-form-heading ${signInFormTitleStyles}`}>{title}</h1>}
+      {title !== false && <h2 className={`juno-sign-in-form-heading ${signInFormTitleStyles}`}>{title}</h2>}
 
       {errorMessage && <Message variant="error" text={errorMessage} className="jn:mb-4" />}
 
diff --git a/packages/ui-components/src/components/SignInForm/SignInForm.test.tsx b/packages/ui-components/src/components/SignInForm/SignInForm.test.tsx
index d371b13c0f..31e4a26f75 100644
--- a/packages/ui-components/src/components/SignInForm/SignInForm.test.tsx
+++ b/packages/ui-components/src/components/SignInForm/SignInForm.test.tsx
@@ -43,15 +43,15 @@ describe("SignInForm Component Tests", () => {
   describe("Title Prop", () => {
     test("renders default title 'Sign In' when no title prop is passed", () => {
       render(<SignInForm data-testid="my-signin-form" />)
-      expect(screen.getByRole("heading")).toBeInTheDocument()
-      expect(screen.getByRole("heading")).toHaveClass("juno-sign-in-form-heading")
-      expect(screen.getByRole("heading")).toHaveTextContent("Sign In")
+      expect(screen.getByRole("heading", { level: 2 })).toBeInTheDocument()
+      expect(screen.getByRole("heading", { level: 2 })).toHaveClass("juno-sign-in-form-heading")
+      expect(screen.getByRole("heading", { level: 2 })).toHaveTextContent("Sign In")
     })
 
     test("renders custom title when string is passed", () => {
       render(<SignInForm data-testid="my-signin-form" title="Welcome Back" />)
-      expect(screen.getByRole("heading")).toBeInTheDocument()
-      expect(screen.getByRole("heading")).toHaveTextContent("Welcome Back")
+      expect(screen.getByRole("heading", { level: 2 })).toBeInTheDocument()
+      expect(screen.getByRole("heading", { level: 2 })).toHaveTextContent("Welcome Back")
     })
 
     test("does not render title when title={false}", () => {
@@ -61,16 +61,14 @@ describe("SignInForm Component Tests", () => {
 
     test("renders empty string title as empty heading", () => {
       render(<SignInForm data-testid="my-signin-form" title="" />)
-      const heading = screen.queryByRole("heading")
+      const heading = screen.queryByRole("heading", { level: 2 })
       expect(heading).toBeInTheDocument()
       expect(heading).toHaveTextContent("")
     })
 
     test("applies correct styling to title", () => {
       render(<SignInForm data-testid="my-signin-form" title="Test Title" />)
-      const heading = screen.getByRole("heading")
-      expect(heading).toHaveClass("jn:text-xl")
-      expect(heading).toHaveClass("jn:font-bold")
+      const heading = screen.getByRole("heading", { level: 2 })
       expect(heading).toHaveClass("jn:text-theme-highest")
     })
   })
diff --git a/packages/ui-components/src/global.css b/packages/ui-components/src/global.css
index 0765870951..c458c72043 100644
--- a/packages/ui-components/src/global.css
+++ b/packages/ui-components/src/global.css
@@ -1052,6 +1052,45 @@
     @apply jn:text-theme-link;
   }
 
+  h1,
+  h2,
+  h3,
+  h4,
+  h5,
+  h6 {
+    @apply jn:font-sans jn:font-bold;
+  }
+
+  h1 {
+    font-size: 1.69rem;
+    line-height: 1.375;
+  }
+
+  h2 {
+    font-size: 1.56rem;
+    line-height: 1.375;
+  }
+
+  h3 {
+    font-size: 1.44rem;
+    line-height: 1.375;
+  }
+
+  h4 {
+    font-size: 1.28rem;
+    line-height: 1.625;
+  }
+
+  h5 {
+    font-size: 1.125rem;
+    line-height: 1.625;
+  }
+
+  h6 {
+    font-size: 1rem;
+    line-height: 1.5;
+  }
+
   /* adds pointer cursor to buttons to restore tw3 behavior */
   button:not(:disabled),
   [role="button"]:not(:disabled) {
diff --git a/packages/ui-components/src/theme.css b/packages/ui-components/src/theme.css
index f81b5234c0..3281b96937 100644
--- a/packages/ui-components/src/theme.css
+++ b/packages/ui-components/src/theme.css
@@ -1122,3 +1122,45 @@
     --tw-content: "";
   }
 }
+
+@layer base {
+  h1,
+  h2,
+  h3,
+  h4,
+  h5,
+  h6 {
+    font-family: var(--font-sans);
+    @apply font-bold;
+  }
+
+  h1 {
+    font-size: 1.69rem;
+    line-height: 1.375;
+  }
+
+  h2 {
+    font-size: 1.56rem;
+    line-height: 1.375;
+  }
+
+  h3 {
+    font-size: 1.44rem;
+    line-height: 1.375;
+  }
+
+  h4 {
+    font-size: 1.28rem;
+    line-height: 1.625;
+  }
+
+  h5 {
+    font-size: 1.125rem;
+    line-height: 1.625;
+  }
+
+  h6 {
+    font-size: 1rem;
+    line-height: 1.5;
+  }
+}